Addition in held form:

An unevaluated sequence:

Evaluate the expression by applying ReleaseHold:

Display a sum of squares in unevaluated form:

View the unevaluated form of an extracted part:

Issue a message, inserting values with no evaluation:

HoldCompleteForm displays without a wrapper:

See the FullForm expression:

HoldComplete displays the held expression with a wrapper:

Evaluate cannot force evaluation of an argument of HoldCompleteForm:

Use Evaluate to force evaluation of an argument of HoldForm:

Sequence and Splice splicing does not happen inside HoldCompleteForm:

Use HoldForm to allow such transformations:

Upvalues do not work inside HoldCompleteForm:

They do work inside HoldForm:

ReleaseHold removes one level of HoldCompleteForm:

HoldCompleteForm 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:

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

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

Hold 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:

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

Only a literal HoldCompleteForm expression is matched: