A lookup table is just a table whose principle purpose is to provide a "lookup" of valid values such as countries, statuses, shoe sizes or whatever; i.e. the kind of data that is generally created once and then remains static. They are useful for data validation and providing lists of values in applications.
Yes, they can be populated by a stored procedure, or by a data entry form, or by import from a file, etc. - same as any other kind of data.