最少 is an adverb/adjective phrase meaning 'the least' or 'at least'. As an adverb, it sets a minimum quantity or condition (e.g., 最少要三个人 'at least three people needed'). As an adjective, it modifies a noun to indicate the smallest amount (e.g., 最少的钱 'the least money'). Note that the English gloss 'at least' overlaps with 至少 (zhìshǎo), which is more common for that sense; 最少 emphasizes the superlative 'least' more directly.