First class is the most luxurious cabin on a flight. Fly first class, upgraded to first class, the first class cabin.
Many airlines have dropped it, since business class took the customers and the space earns more as seats. As an adjective it simply means excellent, which is the commoner everyday use.
1nounfirst classThe most luxurious cabin on a flight.
“He had never turned left into first class in his life.”
first class is a cabin.