[uncountable] the best and most expensive seats or accommodation on a train, ship, etc.头等座位（或车厢、舱等）◆You can upgrade to first class for €50.你花 50 欧元就能升级乘头等舱。◆first-class travel乘头等舱旅行  ➡  business class in the UK, the class of mail that is delivered most quickly第一类邮件（在英国投递得最快的邮件）◆First class costs more.第一类邮件的邮资较高。◆A book of first-class stamps, please.请来一本快信邮票。in the US, the class of mail that is used for letters and cards第一类邮件（在美国用于投递信件和明信片）