Here are some terms I use to distinguish between different categories in my blog. They may not necessarily match their official definitions.
By the Level of Magic:
High Fantasy: The level of magic is very high. Things such as magic duels etc. might happen. Magical items, magical races and magical locations and dimensions may exist as well. Examples: Malazan Book of the Fallen, Harry Potter, The Lord of the Rings
Low Fantasy: Magical feats are not frequent, very few people or items are magical. Examples: A Song of Ice and Fire,
No Magic: This is when events happen in a fictional world, but there is no magic what so ever. The world is in no way an alternate version of earth. Examples: Captive Prince
By the Morality System:
Light Fantasy: Basically, this is the Black and White Morality. The protagonists are always good and the villains evil. It can lead to the author treating anything the protagonists do as something good and just and anything the antagonists do as evil and unfair. Examples: Sword of Truth, Eragon, The Painted Man
Dark Fantasy: This is Grey and Grey Morality. Neither the protagonists nor the antagonists can be easily considered good or evil, but each might be more inclined toward one rather than the other. Examples: Malazan Book of the Fallen, A Song of Ice and Fire
Grimdark Fantasy: Both the antagonists and specially the protagonists are the kind of people you wouldn’t want to meet in real life. Both can commit acts of incomprehensible evil, and rarely there’s any justification for that. The setting is very dark and bleak. The reader may frequently wish that everyone would just die. Examples: Prince of Thorns, Prince of Nothing
For Science Fiction, just replace Fantasy with Sci Fi and Magic with Highly Advanced Technology.
Note 1: Just having fantasy races in a work wouldn’t put them in High Fantasy (or take them out of No Magic). The races have to have the ability to do magic or supernatural powers associated with them to fit in those categories.
Note 2: The morality system is not defined by what the readers may perceive, but rather the author’s attitude towards the story and the characters. Hence why something like The Sword of Truth is placed in Light rather than Grimdark.