What does “vaw” mean in vim in normal mode (and also “caw” and “daw”)?

I has in vim:

foo barba[r]bar
foo

[] indicates cursor position

and when I use vaw or viw the barbarbar is higlithted. And it is ok.

But I would like understand - why? v is for visual mode, a - i dont know why, and w normaly approach to the begin of new word.

I also checked caw and ciw. First one deletes barbarbar and leave cursor after foo without space, second will leave space after foo, both enters insert mode...

So why it works? Is any referance for this in vim help? Could anyone translate it for vim language?