In Scrabble, this is the name given to any play that uses all 7 tiles. Such a play is awarded the usual point value, plus a 50 point bonus.
Recognizing bingos is a critical part of the serious Scrabble player's game; hundreds of lists have been made of common six-letter combinations (e.g., the SATIRE list, the SALINE list, etc.) out of which a bingo can be made if a single letter is added. Thus, the beginning of the SALINE list might run like this:
SALINE
B: LESBIAN
C: INLACES, SANICLE, SCALENI
D: DENIALS, SNAILED
...and so on.
As a rule of thumb, only play an S or a blank if it's part of a bingo, since these tiles are both rare and useful.