The word “Palestine” has referred to several different entities, at different times. The word likely derives from the “Philistine” people who lived in the territory of what is today Israel, during Biblical times, though the Philistines have no connection to modern-day Palestinians.
In about 135CE, the Romans began to refer to the region of what is today Israel, the Palestinian Territories, Syria, and Lebanon, as “Syria Palaestina” and the name existed in one form or another for the next two thousand years.
Though the land came under various different rulers for 2,000 years, starting in the 1600s, it became part of the Ottoman Empire, which after subduing a Jewish rebellion radopted the name Syria-Palestine.
During World War I, when the British, French and Ottomans were fighting over the territory, “Palestine” referred to what is today Israel, the Palestinian Territories, and Jordan.
When the British Mandate began, they severed what was then Palestine into two different territories: Palestine (the land between the Mediterranean Sea and the Jordan River) and Transjordan (the land of Palestine east of the Jordan River).
During the British Mandate, “Palestinians” referred to both Jews and Arabs who resided in the territory. After 1948, the majority of what was then considered Mandatory Palestine became the State of Israel, with Egypt occupying the Gaza Strip, and Jordan occupying the West Bank. There was effectively no more Palestine after 1948, since the Arabs, who had an opportunity to establish their own independent State of Palestine, declined to do so.
Only in 1965, with the advent of the Arab-Palestinian nationalist movement, Palestine was adopted. The Palestinian nationalist movement took to referring to themselves as “Palestinians” and their eventual state as “Palestine.”
A sovereign “State of Palestine” never existed prior to the establishment of the State of Israel in 1948. The legality of the current “State of Palestine” in modern geopolitics is still widely debated.