Palestine is the modern shortening of "Syria Palaestina," a name given to the Land of Israel by the colonial power of Ancient Rome, out of spite for the indigenous Jews (Israelites) who rebelled repeatedly, because they didn't like being colonized. The Roman occupiers drew their inspiration from the even more ancient Pelishtim (Philistines), a coastal tribe frequently at war with the Israelites, and whose name literally translates from Hebrew to English as "Invader."
Fast forward a few thousand years, and the descendants of Arab conquerers took the name for themselves, "Falastin." And now, we live in a bizarro world where terrorist groups regularly slaughter Jews (and whoever else happens to be standing in the way) in order to end the Israeli occupation of Israel and secure freedom (from Jews) of the indigenous Invaders.
Confused? We don't blame you. What we do know is this: Palestine is the homeland of the Jewish People, and after a war of independence that it sparked by the unforgiveable crime of EXISTING, it was decolonized and reclaimed its former name.
What you hear them shouting for a "Free Palestine," ask them: Free of what?
Millions of Israelis are Arab Muslims, free to live and worship as they choose. Does "Palestine" extend that same right to Jews?
The flag in this design was a proposed version of the Israeli flag from the time of the Yishuv (the return of Jews from two millennia of exile to their ancestral home), an unofficial Flag of Palestine during the late British Mandate. Why use this flag? Honestly, we just thought it looked cool.