Conditions

Blinded

A blinded creature can't see and automatically fails any ability check that requires sight.
Attack rolls against the creature have advantage, and the creature's attack rolls have disadvantage.

Burning

A Burning creature has disadvantage on Concentration Saving Throws. Burning comes in stacks, and for each stack of Burning a creature has at the start of its turn, it takes 1d4 damage of a type listed by the effect which caused the Burning, (usually fire). After this, the Burning creature loses one stack of Burning.
As a Bonus Action, the Burning creature, or another creature within 5ft of it, can make a DC13 Dexterity (Slight of Hand) check to remove one stack of Burning from the creature. This is representative of patting out flames, scraping off acid, or shaking the creature out of a horrifying vision.
Certain effects that cause Burning might list specific ways a creature can or cannot end the effect, however additional ways to stop the burning can be attempted, such as dousing the creature in water, each of them with varying degrees of success depending on the DM.

Charmed

A charmed creature can't attack the charmer or target the charmer with harmful abilities or magical effects.
The charmer has advantage on any ability check to interact socially with the creature.

Deafened

A deafened creature can't hear and automatically fails any ability check that requires hearing.

Exhaustion

Some special abilities and environmental hazards, such as starvation and the long-term effects of freezing or scorching temperatures, can lead to a special condition called exhaustion. Exhaustion is measured in levels. For each level of Exhaustion a creature has, it subtracts that much from any Attack Roll, Ability Check, or Saving Throw the creature makes.
If an already exhausted creature suffers another effect that causes exhaustion, its current level of exhaustion increases by the amount specified in the effect's description.
An effect that removes exhaustion reduces its level as specified in the effect's description.
A creature that falls Unconscious from being reduced to 0 Hit Points gains 1 level of Exhaustion.
At the end of a long rest, provided that the creature has also ingested some food and drink.

Frightened

A Frightened creature cannot willingly move close to the source of its fear
The creature has disadvantage on saving throws imposed by the source of its fear, and the source of its fear has advantage on attacks against it.
The creature also has disadvantage on Ability Checks while it can see or hear the source of its fear.

Grappled

A Grappled creature's speed becomes 0, and it can't benefit from any bonus to its speed. The condition ends if the Grappler is incapacitated (An incapacitated creature can't take actions or reactions).
The condition also ends if an effect removes the grappled creature from the reach of the grappler or grappling effect, such as when a creature is hurled away by the thunderwave spell.

Incapacitated

An incapacitated creature can't take actions or reactions.

Invisible

An invisible creature is impossible to see without the aid of magic or a special sense. For the purpose of hiding, the creature is heavily obscured. The creature's location can be detected by any noise it makes or any tracks it leaves. Attack rolls against the creature have disadvantage, and the creature's attack rolls have advantage.

Paralyzed

A paralyzed creature is incapacitated (An incapacitated creature can't take actions or reactions.) and can't move or speak.
The creature automatically fails Strength and Dexterity saving throws.
Attack rolls against the creature have advantage.
Any attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature.

Petrified

A petrified creature is transformed, along with any nonmagical object it is wearing or carrying, into a solid inanimate substance (usually stone). Its weight increases by a factor of ten, and it ceases aging.
The creature is incapacitated (An incapacitated creature can't take actions or reactions.), can't move or speak, and is unaware of its surroundings.
Attack rolls against the creature have advantage.
The creature automatically fails Strength and Dexterity saving throws.
The creature has resistance to all damage.
The creature is immune to poison and disease, although a poison or disease already in its system is suspended, not neutralized.

Poisoned

A poisoned creature has disadvantage on attack rolls and ability checks.

Prone

A prone creature can only move by crawling, while crawling a prone creature gains Slowed 1 (the creature spends 2 feet of movement for every 1 foot it moves.).
A prone creature can stand up using half of its unaltered walking speed.
The creature has disadvantage on attack rolls.
An attack roll against the creature has advantage if the attacker is within 5 feet of the creature. Otherwise, the attack roll has disadvantage.

Restrained

A restrained creature's speed becomes 0, and it can't benefit from any bonus to its speed.
Attack rolls against the creature have advantage, and the creature's attack rolls have disadvantage.
The creature has disadvantage on Dexterity saving throws.

Slowed

A creature can have multiple copies of Slowed, and certain effects can give multiple of these copies. If a creature gains additional copies of Slowed, they add onto the previous stacks of Slowed. A Slowed creature spends X feet of movement for every 1 foot it moves, where X equals one plus the number of stacks of Slowed the creature has.

Stunned

A stunned creature is incapacitated (An incapacitated creature can't take actions, bonus actions, or reactions), can't move, and can speak only falteringly.
The creature automatically fails Strength and Dexterity saving throws.
Attack rolls against the creature have advantage.

Unconscious

An unconscious creature is incapacitated (An incapacitated creature can't take actions or reactions), can't move or speak, and is unaware of its surroundings.
The creature drops whatever it's holding and falls prone.
The creature automatically fails Strength and Dexterity saving throws.
Attack rolls against the creature have advantage.
Any attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature.