Paleolithic describes the Old Stone Age — the very long time, thousands and thousands of years ago, when people made tools and weapons from stone, before farming. Archaeologists split the Stone Age into Paleolithic (the oldest, chipped stone), Mesolithic, and Neolithic (newer, with polished stone and farming). So a Paleolithic tool is a very old stone tool, and Paleolithic people hunted and gathered; they did not grow crops yet. It is a school and museum word, not everyday chat. People often capitalise it (Paleolithic) because it is the name of a period. American English usually writes paleo-; British English often writes palaeo- (Palaeolithic).