What is usermeta function in Wordpress?

The user metafunction is used to retrieve the metadata of users. It can return a single value or an array of metadata.

Syntax is: get_user_meta( int $user_id, string $key = '', bool $single = false )

User id is the required user id parameter

Key is the optional parameter which is the meta key to retrieve. By default, it returns data for all key values.

Single is an optional parameter that tells whether the single value will return. By default, it is false.