Sokan

"It's over, Anakin. I have the high ground!"

―Obi-Wan Kenobi to Darth Vader^[src]

Sokan was more of a principle of lightsaber combat than a true form.

Developed by the ancient Jedi Knights during the Great Hyperspace War, Sokan teaching revolved around using the environment itself to gain a tactical advantage in combat. Sokan involved maneuvering so that swift strokes of the lightsaber could be aimed towards the opponent's vital areas, using quick tumbles, jumps, and movements. Combatants made use of large amounts of terrain, trying to maneuver their opponents into vulnerable areas during the course of battles that involved Sokan techniques. This technique allowed for great speed and mobility and left no openings in one's defense.

Although it was unclear whether Obi-Wan Kenobi received formal Sokan training or not, the Jedi Master did employ elements of Sokan while dueling Darth Vader on Mustafar. Towards the end of the duel, Obi-Wan sought the high ground and used his favorable positioning to defeat Vader, attacking his weak points. This was the factor that led to Vader's defeat, and, in his battle against Luke Skywalker on the second Death Star, may be a reason why he threw his lightsaber when Luke got the high ground instead of going after him.