a broken piece: a fragment, especially a piece of bread broken off from a loaf
This word comes from the verb κλάω, "to break," and it names the result of that action: a piece that has been broken off from something larger. It is not a word for any small bit but specifically for a broken-off portion.
In the New Testament it appears only in the accounts of Jesus feeding the crowds, and always in the plural: the leftover pieces gathered up after everyone had eaten their fill. The Gospel writers carefully count the baskets, twelve after the five thousand and seven after the four thousand, so the fragments become a way of measuring how far the miracle overflowed the need.
It is worth keeping the word apart from two neighbors. A crumb (ψιχίον) is the tiny scrap that falls from a table; a fragment here is a substantial broken portion, enough to fill baskets. And a fragment is not the whole loaf but a part broken from it.