A swingman in basketball is a term used to describe a player who has the skillset to play as either a shooting guard (SG) or a small forward (SF). Swingmen are also commonly referred to as "wings," "guard/forwards," or "tweeners."
In the NBA, these are usually players who in the 6'5" to 6'9" range. At this size, a good swingman is neither overpowered by forwards nor too slow to keep up with guards. A good swingman must possess both strength and quickness to keep up with either set of players.
It is common for swingmen to be scoring machines on offense. Scoring is an important part of both the shooting guard and small forward positions, so it is expected that a swingman can contribute on the offensive end.
A swingman in an important role on any basketball team because they give a coach more personnel grouping options-if a coach feels their team needs more length, the swingman can be used as a guard; and if a team needs more quickness, the swingman can occupy a forward spot.
The term "swingman" was invented to describe John Havlicek. Since then, it's been used to describe many famous players, including Clyde Drexler, Kobe Bryant, and George Gervin. Some modern examples of swingmen in the NBA are Paul george, Jimmy Butler, and Gordon Hayward.