What does "float mana" typically mean?
mana floating is a slang mtg term and refers to mana left over after you play a spell.


  Refers to mana added to a player's mana pool and not used immediately.
  For example, a player might tap all of his or her lands for mana, then
  play Armageddon (destroying all land in play), then use the excess
  "floating" mana to play some other card.


http://mtg.wikia.com/wiki/Slang#Float

Talking about floating mana does not imply that you are about to pass priority. This is because you can play multiple spells before you pass priority and you would potentially have mana left in your pool between such plays. After casting each spell you need to make it clear how much and what type of mana you still have in your pool, so talking about how much and of what types of mana are still floating seems appropriate.

In a tournament, as long as your usage is clear and consistent there should be no problems.