second class noun
Learner's definition of SECOND CLASS
1 [noncount]
a : a level of service on a train, ship, etc., that is just below first class（火车、轮船等的）二等座；二等舱 b : a class of mail in the U.S. that includes newspapers, magazines, etc.第二类邮件（在美国用于邮寄报纸、杂志等）
c : a class of mail in the UK that costs less and takes longer to arrive than first class第二类邮件（在英国指比第一类邮件邮资低、投递慢的邮件）
2
[singular] British : an undergraduate degree of the second highest level given by a British university（英国大学本科的）二等成绩学位