the identity operation
The identity is the 'do nothing' move, or, if you prefer, turn the object a full 360 degrees so every atom comes back exactly where it started. It sounds trivial, but every object has it, even a shapeless blob, and it plays the same role as the number 1 in multiplication or 0 in addition: the neutral member that changes nothing.
Why bother naming nothing? Because symmetry is described by groups, and a group must contain an identity so that every operation has something to combine with and return to. Written in the international (Hermann-Mauguin) notation it is 1 (a 1-fold axis, a full turn); in Schoenflies notation it is E (from the German Einheit, unit). A crystal whose only symmetry is the identity belongs to point group 1 (Schoenflies C1), the lowest symmetry there is, found in the triclinic system.
Practically, the identity is what makes the counting work. Combine any operation with its inverse and you land on the identity; that closure is what lets the 32 point groups and 230 space groups be exact, finite lists rather than open-ended collections.
Point group 1 (C1) contains a single operation: the identity. A triclinic crystal with a completely lopsided motif has exactly this and nothing more.
The identity leaves every atom where it is, the neutral 'do-nothing' operation.
Do not confuse the identity 1 (a full 360 degree turn, symbol 1) with the inversion centre (symbol 1-bar). They look similar in the symbol but do opposite-feeling things: one changes nothing, the other flips the object through a point.