Question regarding GTypeValueTable

["David Shultz" <mrbraz97 gmail com>]

I was looking at the api and came to a section
http://www.gtk.org/api/2.6/gobject/gobject-Type-Information.html#id2884668

that explains GTypeValueTable structure. It talks about
collect_format member and says "Each character in
the format represents an argument to be collected"
what is this argument? Does it mean an argument
to a function? if yes of what function?
Thanks.