Did the Buddha ever define what he meant by "self"?

*Added: I am asking this because I am not sure if anything I observe would be considered "self" according to the Buddha. I don't have this problem with craving or suffering because I can observe/experience craving and suffering and it seems quite clear that they can be and are defined as such.* It seems to me I am unable to determine whether there is, isn't, what is or what isn't "self" because I don't know what aspect/s of reality the word "self" is defined as corresponding to. I am wondering if it is possible to describe what aspect/s of reality the word "self" is defined as corresponding to. It looks like the Buddha may have defined the aggregates as "not-self" so if there is a "self" (What is a "self"?) then according to the Buddha it's definitely not the aggregates. In my opinion this cannot simply be a "view for practicality" because then the Buddha would be a liar in that case.