noun

• (uncountable) The act of accelerating, or the state of being accelerated; increase of motion or action; as opposed to retardation or deceleration.
• (countable) The amount by which a speed or velocity increases (and so a scalar quantity or a vector quantity).
• (physics) The change of velocity with respect to time (can include deceleration or changing direction).
• The advancement of students at a rate that places them ahead of where they would be in the regular school curriculum.