Everything; this and that; a phrase that refers collectively to many things or causes (used in both positive and negative contexts).
それもこれも君が忙しかったからだよ。
It's all because you were busy.
新しい仕事でそれもこれも覚えなければならない。
At my new job I have to learn all sorts of things.
値段も高いし、それもこれも不満が出てきた。
The price is high, and all sorts of complaints started to appear.