Trainspotting was a funny, harrowing, even philosophical film about, in the main, heroin abuse. Oddly it contained no references to actual trainspotting. In fact, there's only one train in the whole film, and if you blink, you'll miss it. This entry is not about that film.
Trainspotting is a hobby. The participant's aim is to 'spot' as many as possible of the various locomotives on the nation's railway network1. Each of these vehicles has a unique number, and the trainspotter will either write these numbers down in a notebook, or cross them off a list of numbers in one of the many handbooks available which list all the active units at a given time. And that's it.
Railway enthusiasts, like many hermetic orders, have developed a slang all their own. Here are a few examples of this surreal and utterly incomprehensible2 language.
Several Gems include:
Spoon - Presumably refers to a Brush Type 4 (Class 47) for seemingly no apparent reason - previously 'Duff'.
Gricer - This is the word used most often by railway employees, and by many trainspotters, to describe trainspotters.
Syphon - Refers to a Class 37 locomotive presumably due to the sound of its air cooling equipment for its diesel engine.
Slug - Has recently supplanted 'Syphon' as the name for a Class 37. Reason unknown.
Gronk - Probably some sort of noise that a Class 08 shunter makes. Hence the nickname.
Rat - Given to the former Class 25 freight locos as they were small and there were that many of them. 327 to be accurate, all now retired.
McRat - Scottish equivalents of the Class 25 - Classes 26 and 27, also now retired.
Crompton - Given to the Class 33 presumably by a Traction Engineer as they use Crompton Parkinson electrical equipment.
Bog Unit - General term for the elder Diesel Multiple Units as their general demeanour, appearance and standard of maintenance (especially in the 1970s) reminded someone of a toilet. Or maybe it was as there were so many of them.
Frajjing - the practice of writing down or crossing off the number of a train one has not in fact spotted - needless to say this is frowned upon as cheating.
Cabbing - gaining access to the cab of a spotted train.
Steam engines are dismissed by some Modern Traction fans as 'Kettles'.
Those who habitually try and traverse every part of the railway system by bizarre and often ancient (or preserved) locomotives are the 'bashing' fraternity.
Trainspotting with any seriousness involves long hours spent on windy platforms waiting for the passage of the next express. Certain equipment is necessary, including pens, notebooks, binoculars, sandwiches, thermos flasks and platform tickets. For this reason, the most practical form of attire for the trainspotter combines windproof and waterproof fabric with copious deep pockets. Hence - anoraks.
Trainspotters are often shunned by 'normal' people as being socially awkward, odd individuals who show undue interest in something the majority of people see as a completely pointless waste of time3. They therefore sometimes cruelly characterise anyone who shows such tendencies by referring to them with the derogatory term 'anorak'.
While trainspotting is the archetype, there are several other common 'spotting' hobbies, involving buses, birds4, and aircraft.
Take a look around the least busy corner of your local large bookshop and you'll find several books and magazines on this kind of subject.