A declarative sentence is a type of sentence that makes a statement or expresses an opinion. It provides information and ends with a period. For example, "The sky is blue" is a declarative sentence because it conveys a fact about the sky. Declarative sentences can be simple or complex, and they are commonly used in everyday communication. They can also be positive or negative, such as "I like ice cream" or "I do not like ice cream." Overall, declarative sentences are essential for conveying clear and straightforward information in language.