Kain was first instructed on the use of Floating in Blood Omen 2. In Chapter 1:Welcome to Meridian, whilst training in the Slums, Kain was instructed on using the ability by Umah. Kain would use it throughout Blood Omen 2, where it was primarily used to aid hunting, allow Kain to silently land nearby Enemies and strike undetected. The ability could also be used to slightly extend the range of Kain's jumping, in the manner used by Raziel's Gliding in the Soul Reaver arc[Blood Omen 2].
Floating returned in Defiance, where it retained it's emphasis on slowing descent, but was presented as much more of an equivalent of Raziel's Gliding ability (despite being referred to as one of Kain's Unique Abilities); Kain's Floating noticeably had a lesser range than Raziel's gliding. Kain would use the ability throughout Defiance and it would be seen in use in the final climactic scenes, as Kain used it to 'sneak up' on an unsuspecting Moebius in the Spirit Forge[Defiance].
The Floating ability is only referred to as 'Floating' in-game, however behind the scenes the ability can be referred to as Floating Descent  or Slow Descent; in some cases it is also named as 'Gliding', despite being equivalent, but not identical to Raziel's Gliding ability (and with the gliding ability referred to as one of Raziel's Unique Abilities)
Floating is unusual as unlike other abilities seen in Blood Omen 2, it is not referred to as a 'Dark Gift' (a distinction it shares with the Whisper and possiblyAbsorbing Veins) despite the term 'Dark Gift' being used extensively (and exclusively) to refer to natural vampire abilities in that game. In Defiance, as with the rest of the Soul Reaver arc, all of these powers are referred to as 'Abilities'.
Floating is an ability that Kain uses extensively but he is never seen to gain in any form; like Fury (and possibly the Whisper), Kain begins Blood Omen 2 with the ability, despite it not being seen in Blood Omen, perhaps suggesting that Kain may have gained the ability between games[Blood Omen 2]. In Defiance, Kain once again begins with the Floating ability[Defiance].
↑ 1.01.1Umah:"Excellent. Know that you also have the ability to float. When you are on a ledge, such as this one, you may land silently and carefully by floating down. This will be important when I train you to kill. Now, follow me." Crystal Dynamics. Blood Omen 2. (Eidos Interactive). PlayStation 2. (March 19, 2002) Transcript.
↑ 2.02.1"Controlling the Game: Glide PS2:X(hold) / Xbox: A(hold)" Prima Games. Prima's Official Strategy Guide to Blood Omen 2(2002). Page 2. ISBN 0-7615-3774-0
↑ 3.03.1"Gameplay ControlsJump + X button: Hold while in mid air for Kain to glide." Crystal Dynamics. Blood Omen 2 manual. pg6 (Eidos Interactive). (2002) Download.
↑ 4.04.1"Floating Descent: When you jump with Kain quickly hold the jump button in mid air to slow your descent and you will glide down instead of falling. This is very useful to allow yourself more time to react as you slowly descend. It is a great way to avoid danger as you land." Prima Games. Prima's Official Strategy Guide to Legacy of Kain: Defiance(2003).Page 11.ISBN 0-7615-4467-4
↑ 5.05.1"Floating Descent: When Jumping or falling, Kain can slow his descent to land silently and with greater accuracy. *While in mid air hold down the X button to slow your descent./ *Release the X button to resume your normal descent." Crystal Dynamics. Legacy of Kain: Defiance manual.pg 17. (Eidos Interactive). (November 11, 2003) Download.