read-variable

read-variable is a built-in function in `C source code'.

(read-variable PROMPT &optional DEFAULT-VALUE)

Read the name of a user option and return it as a symbol.
Prompt with PROMPT. By default, return DEFAULT-VALUE or its first element
if it is a list.
A user option, or customizable variable, is one for which
`custom-variable-p' returns non-nil.