Train spotting is similar to plane spotting, registering the number and model of passing trains in a notebook. It is seen as a nerdy hobby and train spotters have the reputation of being rather socially awkward.

In the movies it is an euphemism for doing drugs as the characters go to the disused Leigh train station where junkies hang out.

Yes. Trainspotting is a (1993) novel by Scottish writer Irvine Welsh. Soon after its publication, the novel was adapted for the stage. The film has been adapted from the stage play by Scottish screenwriter John Hodge.

The title is a reference to an episode from the novel where Begbie (Robert Carlyle) and Renton (Ewan McGregor) meet "an auld drunkard" in the disused Leith Central railway station, where they mean to use a toilet. The drunkard asks them (in a weak attempt at a joke) if they are "trainspottin." Welsh has explained that, when he was growing up in Edinburgh, there was an abandoned train station that had become a place frequented by the homeless and drug addicts. When the drug addicts were going to the station to take drugs, they would often say that they were going "Trainspotting". According to director Danny Boyle, Through the late '80s in Britain, it (trainspotting) began to mean anybody who was obsessive about something trivial, and part of that is drugs. It's a very male thing. Women, they know better. It was a way in which men would conquer an area of life by just knowing everything about all the Sean Connery films.

Sick Boy [Jonny Lee Miller] in the novel has the name Simon David Williamson. Renton refers to him by his real name in a scene that was deleted from the final film. In this film's sequel, Sick Boy is referred to as Simon through most of the story.

The generally-accepted answer is that the baby starved to death. This information comes from the novel and isn't explicitly stated in the film. In the book, it is due to neglect (starvation or dehydration) because of the parents' heavy drug use.

Toxoplasmosis is caused by the protozoan parasite Toxoplasma gondii. It is contracted by eating contaminated meat and vegetables or by touching anything that has been contaminated with Toxoplasma. Cats are particularly notorious for carrying Toxoplasma (obtained from eating rodents and birds), which thrives in their feces. Symptoms of Toxoplasma infection in adults can range from no symptoms at all to general flu-like symptoms. Since the disease crosses the placental barrier, pregnant women are warned to be especially careful around cats and not to clean feces-laden litter boxes, as contacting the disease while in utero can be extremely harmful to a fetus, resulting in miscarriage, stillbirth, eye lesions, retinal damage, mental disabilities, and seizures. In Tommy's case, the disease formed a large abscess (pocket of infected tissue) in his brain that likely caused one or more seizures and interfered enough with his brain function to kill him. For more information about Toxoplasmosis, see here. It is especially dangerous to people who have suppressed immune systems like Tommy, who contracted HIV.

The most likely explanation is that he'd become a heroin addict like his friends and may have shared an infected needle. Another theory could be that in the wake of his being dumped by his girlfriend, Lizzie, he may have had sex with someone who was also infected and contracted the disease that way.

He's hallucinating. Swanney (aka Mother Superior, aka, Johnny Swan) gave him a particularly heavy dose of heroin and Renton wasn't prepared for it. (Renton had also been off heroin for a short period of time, having been enrolled in a methadone program to wean him off heroin. Having been off heroin, the dose that Swanney gave him was a particularly heavy shock to his system.) When he's taken to the ER, they give him a shot of what's likely Narcan, which brings him out of his trip, IE, out of the carpeting.

If Swanney had called an ambulance and the paramedics came directly to his flat, they would have found out that he's a heroin dealer and allows his friends and customers to crash at his flat when they use his product. Subsequently, the paramedics would have called the police, and Swanney would have to either move his operation or he'd have been arrested and tried for dealing illegal substances and he'd lose his clients. The way Swanney sees it—and his clients probably believe this as well—it's better to call a taxi because the driver, who's being paid for his services, wouldn't call the police. He merely drops Renton off at the ER, collects the money Swanney had stuffed into Renton's pocket, and zooms off looking for his next fare.

The concept that highly talented people hit a peak and then their ability to produce quality "product" (music, film, acting performances, sports, etc) declines. Sickboy believes that Sean Connery, a hero of Scotland because he's from Edinburgh, hadn't turned in a decent or good performance since his days portraying James Bond. Renton brings up Connery's nomination and win of the Best Supporting Actor Oscar in 1988 (for The Untouchables), however, Sickboy dismisses it as a "sympathy vote", probably meaning that Connery had been nominated a few or many times in the past and hadn't won. (Think along the lines of Al Pacino being nominated many times and finally winning in 1993 or Martin Scorsese or Steven Spielberg being nominated for the Best Director Oscar and not winning for many years, despite their performances or films being highly praised by critics and fans.) Some of the other people Sickboy mentions, Charlie Nicholas (a Scots footballer), David Niven (an English actor), Malcolm McLaren (known best for being the Sex Pistols manager) and Elvis Presley, had, at least according to Sickboy's opinion, reached their creative peak and then lost their ability to entertain or turn out adequate new material.

If Spud had got the job, then his government welfare cheque -- referred to as a "giro" short for Girocheque, GIRO itself stands for General Interbank Recurring Order -- would be stopped. Spud, Renton and Sickboy, being addicted to heroin, would rather not have regular jobs anyway so they can live their lives any way they see fit.

Put simply, loyalty. We're not given any clue as to how long these guys have been friends so Begbie might not have been such a violent and antisocial person when the crew became friends. But, since they've probably known him for a long time, they feel a certain loyalty to him. His change could have also been very gradual. Or they simply could be scared of what he'd do to them if they ignored him. Plus, he's probably a good footballer, and they need him for their team. It is made clearer in the novel, where we learn that the guys (including Begbie) have been friends since their school days.

The word "habit" used in this way has two meanings. (1) Swanney (whose real name, Johnny Swan, isn't used in the film but is in the novel) has probably been using heroin much longer than Renton's crew. So he's experienced a habitual addiction to it that could be decades-long. (2) A habit is also the word used to refer to the set of garments worn by nuns as a part of their discipline. More can be read about it here. A "mother superior" is the nun in a convent or at a church that serves as a leader of the nuns of the parish.

Danny Boyle's "Trainspotting" was at first released in the USA as a slightly cut R-rated VHS. Two sex scenes and a scene of the leading actor Ewan McGregor putting a syringe with heroine in his vein were removed. The later US releases were uncut yet also with an R rating. For the 18-rated UK VHS by Polygram, also from 1996, two cuts were necessary during the (in)famous drug abuse scene.

They'd tried to steal music and video cassette tapes from a shop in the hopes they could sell them for money to buy heroin. The men chasing them are not actually police officers, but are security guards from the store. The incident is explained more fully in the novel, where they were also trying to steal books to sell too.