third class 
noun [in singular]
1A group of people or things considered together as third best.To you few lacklustre folk in the third class; consider yourselves suspended (until you fix up).
1.1British A university degree or examination result in the third-highest classification: he obtained a third class in part 1 of the geography tripos
1.2 [mass noun] US A cheap class of mail for the handling of advertising and other printed material that weighs less than 16 ounces and is unsealed: third class has been the fastest growing category of mail
1.3 [mass noun] chiefly historical The cheapest and least comfortable accommodation in a train or ship: he grabbed a seat in third class...
- By comparison rail fares were around 1d per mile in first-class and 1 / 2d in third-class.
- Her first passage cost twenty dollars and she and all the other immigrants on board travelled in steerage or third-class.
- It doesn't matter whether you are in first class or third class, but it is essential that you get on the train.
adjective & adverb
1Of the third-best quality or of lower status: [as adjective]: many indigenous groups are still viewed as third-class citizens...
- Set in 1939, the film tells the story of one widow as she attempts to deal with her third-class status in India.
- If not for its efforts, our society and its institutions would still be quite exclusive, and we would still be truly third-class citizens.
- The triumph of the civil rights movement was that it removed the legal practices of segregation, which made black people second and third-class citizens.
1.1 [as adjective] British Relating to the third-highest division in a university examination: he left university with a third-class degree...
- More specifically, every lecturer realises that awarding a third-class degree (or failing a student in a module) means that his teaching methods will inevitably be called to account.
- Distracted from his studies, he graduates with a third-class degree and decides to become a writer.
- She was educated at St Paul's Girls' School and Somerville College, Oxford, where she read modern history and obtained a third-class degree in 1928.
1.2US Relating to a cheap class of mail including advertising and other printed material weighing less than 16 ounces: [as adjective]: third-class mail...
- The divisions operate on a semiannual schedule, sending spring and fall meeting abstracts and newsletters to their members via third-class mail.
- Note of course that filing a change of address or hold in her name is a crime, and a change of address wouldn't stop the third-class mail anyway.
- The print material is sent via first-class mail the same day the video is sent via third-class mail.
1.3chiefly historical Relating to the cheapest and least comfortable accommodation in a train or ship: [as adjective]: a suffocating third-class compartment [as adverb]: I travelled third class across Europe...
- He said the third-class train had no dining car, but that passengers often brought gas cylinders and small stoves aboard despite regulations forbidding it.
- The description of their honeymoon voyage on a third-class train in India is a predictable Orientalist travelogue.
- What, I wondered, were second- and third-class accommodations like?