It genrally means someone who is wise and rightous, who has a strong and good moral intuition and the wisdom to back it up and analyze it to find it to be good. The word itself shares a root/is derived from צדק, which means to do just things or to do what is correct/just/right. A tzadik makes things be as they should be (see also tikkun olam). A tzadik also helps us see the divinity and/or rightousness within ourselves.

I used that word because there are many so called tzadikim that are arguing for israel and its so-called right to defend itself, so im wanting to say that this is not the way forward into rightousness but rather a path that works evil, through genocide and oppression, and a tzadik should recognize this (and indeed some have).

Theres also the argument (at least, ive heard it in my family) that one may be called a tzadik but that no one is a tzadik, at least not in perpetuity; rather, one takes actions as a tzadik would. This shifts the focus onto the actions themselves and recognizes that no one is inherently rightous, rather ones actions are rightous and one is rightous in that situation.