What is the orange tick on the icon attached to a "user"? I am trying to remove 2 users and I think the tick is preventing me from deleting.

When transferring from an older imac, to my new one with mountain lion, I was persuaded to nominate about 3 account names. I really just want the whole lot under the one a/c name. So I am trying to delete 2 user names, but I think the orange ticks prevent me from deleting. Each of these user names is qualified by the description "standard". Help.......I cant find help anywhere else.