Hold[expr] maintains expr in an unevaluated form.
Hold has attribute HoldAll, and performs no operation on its arguments.
Example: Hold[1+1] .
Hold is removed by ReleaseHold.
Hold[, , ... ] maintains a sequence of unevaluated expressions to which a function can be applied using Apply.
Even though expr itself is not evaluated, Hold[expr] may still evaluate if expr is of the form f[args], and upvalues for f have been defined.
See The Mathematica Book: Section 2.5.5.
See also: HoldPattern, HoldForm, HoldComplete, Unevaluated, HoldAll, Symbol.