The word rank has several meanings:

1. A position in a hierarchy or ordering system. In the military, a general holds a higher rank than a sergeant. In school, if you rank first in your class, you have the highest grades. When you rank things, you put them in order based on some quality: you might rank your favorite books or rank pizza toppings from best to worst. Search engines rank websites, showing the most relevant ones first.
2. Having a strong, unpleasant smell. A rank odor might come from spoiled food, dirty gym socks that haven't been washed in weeks, or a garbage can left in the sun too long. The smell is powerful and offensive, the kind that makes you wrinkle your nose and step back.
3. Complete or absolute, used to emphasize how bad something is. A rank beginner has no experience whatsoever. Rank injustice means something profoundly unfair. When someone calls behavior rank hypocrisy, they mean it's an especially obvious and shameless contradiction between what someone says and what they do.

The plural ranks can mean the ordinary members of a group, as in “the ranks of the army” (regular soldiers rather than officers) or “rising through the ranks” (moving up from an ordinary position to leadership).