Depends on your format though.
It is either an attachment in love or an attachment to an email for example a word doc is an attachment.
Here's a quick guess as to why: PCs use the file extension to determine what kind of file a particular file is; Macs use information in the file itself.So if you send, say, a Microsoft Word document...
Its an attachment that goes on your hub. thats what it is. {;-)
A bayonet would be one example.