What do the letters in a postcode mean?

Related questions

1. Why do postcodes change?
2. Can a postcode cover more than one street?
3. How do I change my zip code to postal code?
4. Can two houses have the same postal code?
5. What is postal address example?
6. Can postcodes change?
7. What is the biggest postcode area?
8. Are postal codes house specific?
9. What is a postcode district?
10. Is zip code and PIN code same?

Tags

1. #digits
2. #represents
3. #street
4. #within
5. #represent
6. #working
7. #system
8. #digit
9. #premises
10. #generally
11. #following
12. #hierarchical
13. #postcode
14. #first
15. #district
16. #single
17. #letter
18. #letters
19. #right