The term 'propeller-heads' is a slang term used to describe people who are highly knowledgeable and enthusiastic about technology. It is often used to refer to computer programmers, engineers, and other tech-savvy individuals. The term is derived from the image of a person wearing a propeller beanie hat, which was popularized in the 1950s. The crossword solution for this term is 'NERDS, ' which is another slang term used to describe people who are highly knowledgeable and passionate about a particular subject.