Crew cut hairstyle
A crew cut is a style of cutting the hair that starts with the hair one length in the front and tapers to a uniformly shorter length at or near the crown of the head. The sides and back can actually be of short or medium length, though when most people think of a crew cut, they think of a buzz cut.
Sam Worthington (as Jake Sully in Avatar movie) with a crew cut style.
Military Crew cut
Most people think that the crew cut gets its name from the US military. The truth of the matter is that the hair cut got its name from its adoption by the Yale rowing crew in the 1890s. This hair cut was not adopted by the military until World War II. It was then determined that a buzz cut with the sides and back cut short (high and tight) was a good way to eliminate lice and other pests that like to live in the hair.
Some of the more notable variations on this style include the flat top, the buzz, and the butch. All three of these are classed as short haircuts because the longest hair is generally not over an inch in length. In fact, most cuts range from one quarter inch to three quarters of an inch in length.
When the game of football was first invented, the helmets worn by the players were somewhat flimsy, being made of leather. At that time, football players tended to wear their hair longer. Later, when the switch was made to hard plastic helmets, most teams, starting with Yale's football team, adopted the crew cut for their players.
At some point during the mid 1960s, a man's haircut became a symbol for his political beliefs. Men who wore long hair were considered to be liberal, often referred to as hippies whether they embraced the hippy movement or not. Men with more conservative views tended to wear their hair shorter, with the most conservative adopting the buzz cut.
Ricky Martin long crew cut
Today, unless a man is in the military, it is not overly common to see anyone sporting a crew cut. There are a few, however, who tend to wear some variation on it, either a flat top or a buzz cut. In general, even now, these tend to be men with ultra conservative views as opposed to the more liberal who sport medium to long hair. Long hair does not carry the negative connotations that it did in the 60s and early 70s, but a buzz cut is still the mark of conservatism.