Types of Effects

Characters can receive various temporary or permanent effects that influence, either beneficially or adversely, the affected character's condition.
Such effects can be loosely categorised into three groups:

Damage-over-time effects

Characteristic and parameter modifiers

Control effects

There are two broad categories of negative effects: common and unique. You can learn more about their differences and specific examples by consulting the relevant encyclopedia entry.
A damage-over-time effect deals a certain amount of damage to the afflicted character at the start of their turn.
Such effects can be removed by using items or abilities.
For example, the bleeding effect deals damage at the start of each of the character's turns and lasts indefinitely, but bleeding can be removed with a medikit.
Some damaging status effects: toxin, bleeding, burning, etc. have a number indicating its power.
For example, burning (4) means that this effect will deal 4 damage every turn, until it is removed.
This number can be modified by a variety of talents, abilities, or equipment that can increase or decrease the power of the effect.
You cannot stack the same effect, but stronger sources of the effect override weaker when applied.
For example, if a creature currently suffering from burning (5) is attacked with a flamer with burning (6), it will suffer burning (6) effect. If it is attacked after that with a flamer with burning (3), it will still have burning (6) effect.
Characteristic and parameter modifiers can reduce or boost certain character stats. They generally last a limited time and are removed after a certain number of rounds have passed or at the end of combat. An example of such an effect is blinded, which reduces the character's Weapon Skill and Ballistic Skill by −30 and their dodge and parry chance by −30%.
1 is the lowest possible value of a characteristic. No effect can reduce a characteristic below 1.
Control effects rob the character of the ability to perform certain actions.
These effects always have a limited duration.
For example, the immobilised effect prevents the character from moving.