Ultimate Super Saiyan
Ultimate Super Saiyan, also referred to as Ultra Saiyan or Ultra Super Saiyan, is a Super Saiyan stage midway between "regular" Super Saiyan and Super Saiyan 2. This form holds greater power than the basic Super Saiyan form, but at a cost- the muscles of a Saiyan or a human-Saiyan crossbreed who achieves this stage grow in size as the power levels increase. At the midway point of Ultimate Super Saiyan Stage 2, the Super Saiyan has a balance of increased speed and strength, despite their greater muscle mass. However, at Stage 3, their bulk impairs their speed, making this form ultimately less effective in battle.
Goku, Vegeta, Trunks and Gohan all achieved Stage 2, and used the form during the Cell Games. Goku, Trunks and (likely) Vegeta also achieved Stage 3, but only Trunks actually tried to make use of it in combat, using that stage in battle with Perfect Cell.
Some say that this is also the form that Broly has achieved, but his particular enhanced stage (with white eyes, a green aura, no loss of speed, no intermediary stages, and not being acquired through training) seems to be unique.