A “bye” is simply a request for a player to miss a round without being withdrawn from the tournament.
In person events
For most local tournaments, one 1/2 pt. bye is available for any round that you must miss, if requested before the start of round 2. Additional byes will be at 0- pts. Some multiple-day tournaments will allow additional 1/2 point byes. Requesting byes is not the norm. Most players will play all rounds in an event and request no byes.
Many online events, including tournaments held on ChessKid.com, do not allow byes. Please be prepared to play all games.