Look-up table?

Hi, I''ve been reading here and there about something called a look-up table. It sounds as it''s somekind of table with values (not just numbers mayhaps) and that it''s used to store values for later use, like for a sin/cos look-up table? I''m wondering how this might look in code and what the benefits are? For the sin/cos thingy I think that the benefits are that one wouldn''t have to calculate sin/cos of something each time, since you have it stored you only need to grab it from there. Is that correct? Thanks!