In historical context, member of the nation or tribe of the Philistines in ancient Canaan. Name Palestine is derived from that tribe.

In modern contect, a person who is hostile or indifferent to culture and the arts. Often also include a boorish person or bigot or hypocrite (yeah thank Bible for that, Philistines were the enemy of ancient kingdom of Israel so they got smeared in the book).

Lennin had a friend named Phil and he stopped aging as a teenager. Because of his looks, people kept on insisting he was a teenager, even if they knew better. Lennin got really mad at all of the people that knew better but liked to pretend Phil was a teenager and coined the word Phil-is-teen. He expanded this usage to anyone that spoke falsehoods often that were known to be false.

source: Black Book Of Communism page “Trust me bro”