Sentence:  In the category of categories, \mathbb{CAT}, the objects are categories and the morphisms are <WSD>functors</WSD>. 
Meaning of the word marked with <WSD> tags:  A category homomorphism; a morphism from a source category to a target category which maps objects to objects and arrows to arrows, in such a way as to preserve domains and codomains (of the arrows) as well as composition and identities.