The word "以内" is formed by combining the character "以" (yǐ), which here functions as a preposition meaning "with", "by", or "taking...as a limit", with the character "内" (nèi), meaning "inside" or "internal". Together, they create a compound preposition/postposition that literally means "taking the inside as a limit", translating to "within" or "inside of". It is used to indicate a spatial, temporal, or quantitative boundary, as in "三小时以内" (within three hours) or "预算以内" (within the budget), where the first element defines the scope that "以内" confines something to.