What does economy W mean on Singapore Airlines?

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Tags

1. #saver
2. #selection
3. #segment
4. #following
5. #airlines
6. #forward
7. #booked
8. #under
9. #awards
10. #advance
11. #charging
12. #economy
13. #flexi
14. #extra
15. #begin
16. #legroom
17. #types
18. #singapore
19. #standard