Definitions set boundaries around particular characteristics.
From a certain angle, definitions (or "limits,") can only say what something is not -- and it is "examples" that say what something is.
Consider an ancient scholiast on Dionysius Thrax's Τέχνη Γραμματική (The Art of Grammar):
"And Epíkouros – although he used examples (αἱ ὑπογραφαί) all the time – he shows that limits (οἱ ὅροι) are more valuable, [because he used] limits instead of examples in his work of his natural philosophy lecture: while dividing everything into atom and void by using limits – and while saying that an atom is a solid body having no share of interposition with the void. Void is an intangible nature, that is, untouchable."