It would help if you said what your interests are. I sometimes hang out on lowendspirit.com (self-hosting on cheap servers) and on budgetlightforums.com (flashlights). The OG flashlight forum (candlepowerforums.com) is still around too, but has slowed down a lot. Or heck, start your own!
As other people have explained, basically it’s a viewpoint supporting the existence of Israel. Israel itself is sometimes called “the Zionist entity” as a propaganda term by its opponents/enemies, as a way of refusing to say the name “Israel” or acknowledge it as a country. You might have heard the term used that way and picked up the undertone. It’s like saying “the orange-haired figure” as a way of pointedly refusing to say the name Trump or calling him the president.