"Buccaneer" is a term applied to a specific group of 17th European settlers in the Caribbean who traded with non-Spanish societies. "Pirate" is an umbrella term that is applied to all crew members who primarily live their lives aboard ships that aggressively pursue and rob water vessels.
The majority of buccaneers eventually adopted a life of piracy as a way of garnering wealth. To add to the complication of terms, privateers were mercenary type figures who were specifically employed by a government to act as pirates. Spoils obtained by the raids of privateers technically belonged to the governments by whom they were employed. Privateers, like buccaneers, eventually came to understand that by simply being pirates, they could keep whatever they accumulated and eliminate the need for government subsidized employment. By the end of the 18th century, pirate, buccaneer and privateer had become interchangeable and were used synonymously because almost all buccaneers and privateers were also pirates, but not all pirates were necessarily buccaneers or privateers. "Buccaneer" is French in origin with a somewhat vague etymology and meaning. Most scholars agree that it refers to a French word used to describe someone who consorts with those below their status in life.