A play-in game is a game, usually played at the beginning of a tournament or just prior to the tournament depending on how the tournament is defined. In a play-in, the lowest qualifiers and/or participants who have earned conditional qualification compete for qualification to the main portion of the tournament.
A preliminary game is a game, typically played at the start of a tournament or just before it begins depending on how the tournament is structured. In a preliminary round, the lowest-ranked participants and/or those who have earned conditional qualification compete to gain entry into the main tournament.