There are 4 types of effects in battle which are presented in blue, yellow, red and green colour.
Blue buffs are unique negative or positive effects  that are special for a spesific heroes. They can not  be dispelled.
Green buffs are common positive battle effects  that a lot of different heroes possess. They  can be dispelled.
Taunt is the yellow positive battle effect.  It is also unique as only defenders can cast it. .
Debuffs are negative battle effects that  are  coloured red and could also be dispelled.
Black debuff is a unique negative effect that could be only met in guild raid "The Depths  of Black Machinery". It   can not be dispelled.
Buff is a positive effect that a hero have and can cast on oneself or other heroes in the team.
There are several buff types, for instance, Turn Meter Gain or Crit Damage Increase.
Casting buffs comes in handy in battles and often can decide the outcome of the battle.

While in the battle, you can tap and hold the Buff icon and read what it does.

There are a lot of various buffs in the game. Most of them are common, and some are unique for a certain race or even hero. Here is a full list of buffs: