y'all is a common idiom in the southeastern US as well as Texas. It is a contraction of 'you all' and can mean an individual or one or more members of a group.

y'all is a common idiom in the southeastern US as well as Texas. It is a contraction of 'you all' and can mean an individual or one or more members of a group. all y'all by comparison is generally agreed to mean everyone in the group and can be a replacement for the phrase every last one of you