Boost in Burnout 2: Point of Impact is the original, classic form of boosting. It is very similar to Speed boost in the later title Burnout Paradise. It was also brought back for the final PS2 title Burnout Dominator, but with slightly different rules.
The boost mechanism for Burnout 2 is a continuation of the mechanisms used in the original Burnout. Boost is earned by performing Near Misses, Drifts, and Oncoming. However unlike in the original game, Boost can also be earned by getting air time. However the Boost cannot be used until the Boost meter is completely full. If the boost runs out or the player lets go of the Boost button, they will have to refill the Boost meter to use it again.
Like in the original game, however, the player can perform Burnouts. When the player is Boosting, they can continue to perform boost-earning maneuvers. When the player uses up all of the boost, the meter will refill a certain amount, depending on how much boost earning they did. If the player manages to make the boost refill completely, they will be able to continue boosting. Burnout Dominator would name this technique Boost Chaining.
In the original Burnout, Boost was hard to earn because it was slow to fill. This has been augmented in Burnout 2 by making the boost quicker to fill when performing stunts.