A proposition is a statement that expresses an idea or assertion that can be either true or false. In logic, propositions are fundamental units used to build arguments and reason about various topics. They can be simple, like "The sky is blue," or complex, involving multiple statements connected by logical operators. In mathematics and philosophy, propositions play a crucial role in formal reasoning. They help in constructing proofs and understanding relationships between different concepts. For example, in mathematical logic, propositions can be combined using operators such as "and," "or," and "not" to form more complex statements that can be analyzed for their truth values.