From CS2800 wiki
Definition: Equivalence class
If equivalence relation on a set , then the equivalence class of by (written ) is the set of elements with .is an
In other words,
Note: I usually use the symbols [ and ] instead of ⟦ and ⟧, but the wiki syntax makes this difficult. You may use either notation.When is clear from context, we just write ⟦a⟧.