Define values and attributes for a symbol:

Clear values and attributes:

Clear any old definitions before making new ones:

Unprotect and clear all symbols in a package, to allow it to be read twice:

ClearAll[pattern] clears the same symbols as ClearAll/@Names[pattern]:

Clear does not remove attributes, defaults or options:

Use ClearAll to clear everything:

Clear does not remove messages:

Use ClearAll to clear messages:

ClearAll removes all properties and definitions but leaves the symbol intact:

Remove removes the symbol completely:

Use Unset (=.) to clear definitions with a particular left-hand side:

Clear all definitions and properties:

ClearAll has the attribute HoldAll:

This clears symbol itself:

This clears its value:

Protected symbols cannot be cleared:

Use Unprotect to clear definitions of protected symbols:

Clear can clear the values and definitions for locked symbols:

ClearAll does not affect locked symbols:

When using a pattern without a context mark, all matching symbols on $ContextPath are cleared:

The symbol xy was cleared, along with attempts to clear several system symbols:

Use a pattern with an explicit context mark avoid potentially matching symbols from system or other contexts: