It looks like a lower-case epsilon, but the Wikipedia page on epsilon states that they are not the same.
Does this symbol have a typographic identification outside of mathematics? Where did the symbol come from?
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It only takes a minute to sign up.Sign up to join this community
This is the membership relation, but in set theory this is also known as the epsilon relation, and historically the notation was indeed $\varepsilon$.
(For example, I have the book from 1948 by Tarski and Jonsson Cardinal Algebras where such notation is employed.)
According to this page it was Peano who used epsilon. I suppose somewhere around the 1960's or so, when typography was easier to modify the symbol was taking the modern shape of $\in$ (Bourbaki in their set theory book, ca. 1970, were using $\in$).