*By meaningless I mean undefined, and by meaning I mean definition.
As a student of philosophy, I, like the general public, thought that my difficulty in understanding the concepts of philosophy is because of their deep meaning. But after studying Wittgenstein's philosophy, I am afraid to believe that the difficulty in understanding the concepts of philosophy is not because their meaning is deep but because there is no meaning in them. Because unlike physics and STEM subjects which give rigorous definitions, philosophy gives poor definitions.
Idea: Ideas are usually construed as mental representational images of some object.
Mental representation: A mental representation is a hypothetical internal cognitive symbol that represents external reality
Symbol: A symbol is an object that represents, stands for or suggests an idea, visual image, belief, action or material entity
Quite frankly, I think that's like saying "asdasdasd" means "not dsadsadsa". Not only "asdasdasd" is meaningless, but also any sentences that uses that word is also meaningless. Saying "idea exists" is comparable to saying "asdasdasd exists".
***I hope you know I'm not underestimating philosophy by saying it is not worthy. I'm just thinking if philosophy lacks rigorous definitions.