What ∊ means
It says that an item belongs to a set.
In x ∊ A, read it as “x belongs to set A.”
Peano used an epsilon-shaped membership sign in 1889, an abbreviation for Latin est (“is”). Russell said he was using Peano’s sign in 1903; the printed form appears to be the crescent-shaped epsilon, not clearly today’s ∈. ∊ itself arose in Math Pi fonts for mathematical notation as a distinctly smaller form of ∈.
Don't confuse it with
1Questions people ask
1Why does ∊ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ∊
∊\220ACodes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.

