Unevaluated

Unevaluated[expr] represents the unevaluated form of expr when passed as an argument to a function.

Examples

Pass unevaluated expression:

Length[Unevaluated[1 + 2 + 3]]
(* 3 - counts Plus arguments *)

Get head of unevaluated:

Head[Unevaluated[{1, 2, 3}]]
(* List *)

Head[{1, 2, 3}]
(* List - same result here *)

Please visit the official Wolfram Language Reference for more details.