What is RolePlaying? That question have different answers, depending on who and how you ask. Ask a psychologist/psychiatrist and you will get a medical answer. Ask a "gamer" and you will get another answer entirely. This is what Longman's "Dictionary of Contemporary English" has to say on the subject:
role playing /'- ,--/ noun, uncountable: the act of behaving in the way of someone else or of an imaginary person, either unconciously or for the purpous of learning a job, learning how to behave in certain situations, et.c.
Personally I miss the entry saying that "it can also be a method of (self-)entertainment", or hobby. Perhaps that is what they mean with the "et.c.". So what is the form of roleplaying I'm thinking of? It can be explained as "theatre for the inner eye" or "a game of dice and paper". The RolePlaying Games (or RPGs for short) that I like is played by a group (4 to 6 people, sometimes more, seldom less) of people sitting around a table with one designated "Game Master" (who is responsible for keeping track of the rules and the world/enviorment. In some games the title for that duty is different) and the others taking part through a character. The GM (short for Game Master) will give the player information about what is happening around and to the character, or PC for Player's Character. The players then decide and tell the GM what their PC is trying to do (and sometimes how as well). The GM will then have to judge how to procede. There are 3 options,
1st: Automatic Success. (PC does whatever he wanted to, which is often the case for very simple tasks, and mostly the GM doesn't have to say this is the result of attempt, such as getting out of bed, eating breakfast and brushing one's teeth.)
2nd: Automatic Failure. (The PC will fail what he is attempting if he doesn't change his method to achieve the result. Examples might be trying to climb lighting. These are mostly quite obvious as well.)
3rd: Random Success/Failure. (This means either the GM or the player will have to roll one die or a set of dice, and depending on the result it will be either a success or a failure. Some RPGs use cards, or other methods of randomness, but the goal is still the same: Resolve a random situation. Things as combat, reckless driving (be it space-craft, racing car or horse-and-buggy) most often fall into this category, but it's up to the GM to decide otherwise.)
When one or more of the players have described the actions of their PC's and the success-rate have been determined the GM will explain the new situation. This is also the time when the GM tells what the non-player characters (that is, other beings present at the same location as the PC's, be it the helpful pixie, the indifferent barkeeper or the hostile spacemonster) do (or fail attempting). It is then the players' turn to decide (and tell the GM) what to do next (or at least what to attempt next).
There are other forms of RPG, but as this is the form I like. I'll leave the other forms to be explained of those who are more knowlageable.
My two favourite games are Hârn, which is a medieval/fantasy RPG, and GURPS, which is supposed to be "anywhere, any time, any background". Multi-Background RPGs loose a little for each background, but gains width in "where, when, how". The constructors of GURPS made a good job, although I miss the metrics.