[plural] [noun] [informal]I cleaned the insides (of the pot) with scouring powder.(informal) Your insides are your stomach and other digestive organs .I don't know what's wrong with him but I think it's something to do with his insides.The insides of the cow are used to make dog food.
INSIDES
Meaning of INSIDES in English
Cambridge English vocab. Кембриджский английский словарь. 2012