Science fiction is sometimes divided into two main types - "hard" or "soft" science fiction.

Originally, the distinction was as follows -

Hard science fiction involved the "hard" sciences - physics, chemistry, astronomy, geology.  Hard sciences generally involved fairly definite statements about the universe, and more certainty about our knowledge.

Soft science fiction involved the "soft" sciences - biology, sociology, anthropology, archeology.  Soft sciences were usually more "messy" with less certainty about what we thought we knew.

But this distinction has started to blur over the last thirty to forty years. 

We still sometimes refer to "hard" and "soft" science fiction, but the distinction now depends more on how important science is to the story.