Boxer briefs or some may call them tight boxers are men’s underwear. They are like boxer shorts but tighter-fitted, like briefs. They were introduced in fashion by John Varvatos, when he was still working for Calvin Klein. Some people may find briefs too restrictive but others may find boxer shorts too loose. They are usually made of a combiantion of cottton and spandex.
Boxer shorts are on the other hand also called loose boxers. They are typical men underwear. Most boxer shorts have a fly in front. They close it usually with metal snaps or a button or two.
Some studies have suggested that tight underwear and high temperature are not optimally conductive for sperm production. The testicles are outside the body for cooling because they operate for sperm production at a slightly lower temperature than the rest of the body, and boxer shorts allow the testicles to operate within the required temperature range. The compression of the genitals in briefs may cause the temperature to rise and sperm production to fall.(Source: Wikipedia)