option

Provides an option that the user can optionally select.

option(<option_variable> "help string describing option"
       [initial value])

Provide an option for the user to select as ON or OFF. If no initial value is provided, OFF is used. If the option is already set as a normal variable then the command does nothing (see policy CMP0077).

If you have options that depend on the values of other options, see the module help for CMakeDependentOption.