The word "凡是" (fánshì) is a compound formed by combining the character "凡," which means "all" or "every" in a general sense, with "是," which means "is" or serves as a demonstrative pronoun meaning "this." Together, they create a fixed grammatical structure that functions as a universal quantifier, typically placed at the beginning of a clause to mean "every," "any," or "all that," and is used to introduce a sweeping condition or premise, implying that the subsequent statement applies to each and every case within the stated category (e.g., "凡是学生，都要遵守规则" – "All students must follow the rules").