Self Blue ?

Can someone explain what this term means. What is "self"?

Self blue usually indicates the blue gene that breeds true. Usually it is a lighter form of blue, almost like a splash but no darker flecks on them. When you bread a self blue to a self blue you get only self blues. Where as with the regular darker blue gene (blue with the dark blue lacing) you can get blue, black and splash out of the breedings.

I am by no means any expert but from what I understand self blue (lavendar) breeds true so self blue to self blue gives 100% self blue chicks where blue doesn't. I may not have it correct but it'll give you a place to start researching