The set is not to provide a definition (Undefined Term), we often use a set instead of what is shared, which means a bunch of things that we can clearly define a member (Well-Defined), or is the meaning of enough.
Sets are no words to define (Undefined Term), we often use a subset of what is shared. Which represents a group of things. We can clearly define membership. (Well-Defined) or is a subset of itself.
Set words to define (Undefined Term), we often use the set instead of things together. Which refers to a group of things. We can define the members have clear (Well-Defined) or is the meaning of the set itself.