DPShot stands for Damage Per Shot, and is used to express the actual damage a tower does to the attacking monster. However, the damage in the game is given us in DPS, wich stands for Damage Per Second, and is used to express the damage that a tower does in one second.
DPS x time to reload (in seconds) = DPShot
Damage per 1 shock/bullet x Shots fiered per charge/salvo = DPShot
The DPShot for Laser Tower is calculated a little different too, as Laser Tower has AoE damage, but also deals constant damage for some time, and then needs some time to reload, pretty mush the same as Tesla Tower and ADT. Laser Towers actually need 1 second to reload, and during that time, it is not firing. Otherwise, Laser Towers fire their beams for exactly 2 seconds. Because of that, the DPShot is calculated the same way as for Sniper Towers, Cannon Towers, and Railguns.
Note: Except for Zafreeti and the Laser Tower, a tiny red number appears on top of a tower or monster when it attacks. This number indicates the damage that the tower or monster inflict per shot. In the case of Zafreeti, a tiny green number appears, showing how much it heals. For some reason, the Laser Tower will not produce a number unless rendered useless by a Candy Jar.