Weapons like machine guns can fire quick bursts of bullets. They are fired in quick succession with a belt of ammunition, unlike cannons that can only fire once before they need to be reloaded.
A weapon with the Burst special rule has the “burst” keyword, followed by a number in parentheses. That number indicates the number of shots the weapon can fire in a single turn.
burst(3) would mean that the weapon can be fired three times as a single interaction, a “burst”. For each shot in the burst, the player of the shooting tank makes a separate Roll to Hit.
If the weapon also has the Reload rule, it comes into effect after the entire burst has been fired.