The world record (or WR) for an official event is the best known result achieved in an official solve in competition for that event, up to a certain point in time. This is accompanied by an official world rank of 1 in that event, and is thus the highest possible honor a solve can have. Although world records usually do not last for more than a year or so, the Fewest Moves record of 28 moves stood for about three years until it was broken in 2008. A time which ties the current world record is also considered to be a world record.
The WR for 3x3 is considered by far the most important, because it is the most popular event for cubers and non-cubers alike. The WR single time for this event has, however, recently been held by a lucky solve (that is, one which skipped a step), so it is not the best measure of speed.
Sometimes the world record is abbreviated OWR to distinguish it from UWR, or the Unofficial World Record. This is the best known result (usually required to be non-lucky) achieved out of competition, which is almost always the top result in the unofficial record list at speedcubing.com, which is considered to be the most 'official' unofficial record list. Achieving and submitting an unofficial record for an official event (or a small number of others) earns a mention on the news page of speedcubing.com, which will be seen by a large number of cubers and is thus highly sought after.