What %1$s means?

cart

I want to translate some Vanilla definitions to my language and it may sound noobie but I don't know what %1$s, %2$s,%3$s.....mean. Like in : %1$s accepted %4$s invitation for membership.
I found out only that %1$s means "you" but about the rest ...

Thanks for any help!

luc

=> http://vanillaforums.org/discussion/comment/142351#Comment_142351

luc

=> http://vanillaforums.org/discussion/comment/142351#Comment_142351

cart

=> http://vanillaforums.org/discussion/comment/142351#Comment_142351

thanks!