Vimscript : What is the difference between let g: , let b: , etc.?

Question

I often see in vim plugin something like these :

let g:variable
let b:variable
let l:variable

I made a long research on the vim documentation and on the Internet about these letters 'g', 'b', 'l', but I found noting.

So what is these letters corresponding to ? And what is the complete list of letters ?

Answer 1

b: local to the current buffer

l: local to a function

g: global

:help internal-variables