(PURPOSE) [noun] [U] - a purpose or reason for doing somethingThe idea of this game is to get rid of all your cards as soon as you can.The whole idea (= only purpose) of advertising is to make people buy things.The idea behind the new national lottery is to raise money for good causes.
IDEA
Meaning of IDEA in English
Cambridge English vocab. Кембриджский английский словарь. 2012