A declarative sentence states a fact. This word can be used to describe any action or speech that makes a statement.
"I love the Red Sox!" is a declarative sentence — you're claiming or asserting something. Declarative sentences are the opposite of questions. Known as a "mood" in the grammar world, you can also use declarative to describe other things that make a definite statement. A strongly worded political sign could be declarative. A tone of voice could be confident and declarative. Even a bold outfit could be declarative of your unique style.