Makruh (مكروه) means disliked or discouraged. It sits between halal and haram: doing it is not a sin, but avoiding it is better.
The Hanafi school distinguishes makruh tanzihi (mildly disliked) from makruh tahrimi (close to forbidden, and treated as something to avoid). This is why, for example, crab is described as makruh in the Hanafi school.