What is an IO?

Hello,
I am an Affiliate marketer and looking for Advertisers that I can generate leads for. however, they’ve been asking me for an IO and some information. But What is an IO? I tried googling and i can’t even get the term right. seems like majority, it means ION as in the elemental object thing.
Thank you and i hope for a great answer.
Regards!

See original post by Spatoinks