Bonus Attack Speed

is a Weapon Stat that affects the speed of the player's attack rate by reducing the | damage immunity frames of the entity hit.

It can be increased by holding items and wearing Armor with certain Reforges.

The maximum hits per second with and  can be calculated using this calculator:

Mechanics
decreases the number of invulnerability ticks an enemy is granted upon hitting them.

The formula for the invulnerability ticks of an enemy on hit is:

$${\forall BAS \in [-99,100], hurtResistantTime = \lfloor \frac{10}{1+\frac{BAS}{100}} \rceil}$$

where
 * BAS: Player's Bonus Attack Speed
 * hurtResistantTime: Amount of invulnerability ticks

The max is 100%, doubling the attack rate.

Shortbows
increases the maximum rate of fire of shortbows (Terminator and Juju Shortbow). The default rate is 2 shots per second and is increased up to 4 at 100%.

Trivia

 * Attack speed works on arrows, decreasing the time before another arrow can hit the target. This only applies outside Dungeons, because arrows do not grant invincibility frames in Dungeons.
 * Attack speed does not affect.
 * It is possible to have negative attack speed, and it will lower attack rate.
 * The Livid Dagger and the Zombie Soldier Cutlass are the only items that give 100%.