Tapas (also Tapis) is an old companion to Beer and Wine in Spain. The name comes from the Spanish "tapar" which means "to cover". What it is is usually a split roll (bun), bread or biscuit of some kind piled lightly with some kind of stuff, from vegetables to meat in the manner of an open-faced sandwich. They range from hardly even edible to very delicious.
The practice was started as a way of keeping flies and whatnot out of your beer while the serving wench was bringing it to you. It has evolved into a repast of it's own to the point that there are now such things as Tapas bars. Many people (especially non-Spaniards) consider the idea of Tapas Bar to be pretentious.