Marid
For the water jinn, see Chanti.
Marids (roughly Arabic "rebels") are a type of evil spirit in Islamic theology, comparable to shayatin (devils) and ifrit (rebellious jinn).
Etymology
The term only appears once in the Quran, in 37:7:
6: Innaa zaiyannas samaaa ‘ad dunyaa bizeenatinil kawaakib
("Indeed, We have adorned the nearest heaven with an adornment of stars")
7: Wa hifzam min kulli Shaitaanim maarid.
("And as protection against every rebellious devil")
—Quran 37:6-7
Here marid is used as a descriptor—meaning rebellious—for devils.
In literature outside of the Quran, marids are sometimes considered a type of evil jinn; some even claim they're are the mightiest of the evil jinn.
In some renditions of Arabian Nights the terms marid and ifrit (a class of jinn who are especially mighty and rebellious) are used interchangeably.
The term sometimes has associations with demons, giants, and divs.
So it's not totally clear what exactly a marid is: whether it's another name for devils, another name for ifrit, a subset of devils, a group of evil jinn distinct from ifrit, a subset of ifrit, or what. But everyone agrees they're not fun guys.
D&D
Main article: Chanti
In D&D, marids are water genies, who lean Chaotic Neutral. I'm about 90% sure they're associated with water because marid is reminiscent of marine (coming from Latin mare "sea"). But marid is an Arabic word, not Latin. Marids have nothing to do with water. Therefore, what are called "marids" in D&D are called "chantis" in Marillia. Chantis are the jinn with links to elemental water; and to be clear, they have nothing to do with the marids of Islamic theology. Chantis are pretty chill guys.