Addition in held form:

An unevaluated assignment:

An unevaluated power:

Evaluate the expression by applying ReleaseHold:

Display a sum of squares in unevaluated form:

View the unevaluated form of an extracted part:

Show a formula and its evaluation:

HoldForm displays without a wrapper:

See the FullForm expression:

Hold displays the held expression with a wrapper:

Use Evaluate to force evaluation of an argument of HoldForm:

Sequence splicing and Splice still happen inside HoldForm:

Use HoldCompleteForm to suppress even such transformations:

Upvalues work inside HoldForm:

They do not work inside HoldCompleteForm:

ReleaseHold removes one level of HoldForm:

HoldForm gives an object that is never evaluated:

Copy the output and paste it into an input cell. The 1+2 is still unevaluated:

Defer gives an object whose evaluation is merely deferred until it is explicitly given as Wolfram Language input:

Copy the output and paste it into an input cell. The 1+2 is evaluated:

HoldForm maintains expressions in unevaluated form, and all parts are inactive:

Inactivate maintains symbols in inactive form and allows parts of expressions to be inactive:

HoldForm can be used to freeze the result of ToExpression before it is evaluated:

HoldPattern[expr] is equivalent to expr for pattern matching but maintains expr in an unevaluated form:

HoldForm[expr] is not equivalent to expr for pattern matching:

Only a literal HoldForm expression is matched: