10 codes are used between a select group of friends. Between the group, you come up with 10 codes to use when talking to each other in public when other people are around that you do not want to know what you are talking about/referring to. You create 10 codes amongst your group and share/refer to them when needed.
1.) 1005 - trick
2.) 1012 - ex
3.) 1040 - Mary
Talk in 10 code: Did you see that 1005 he went home with? Filthy!
Talk in 10 code: Why does your 1012 keep sexting you?
Talk in 10 code: 1040! What are you doing? Put it away!