Well it isn't FT terminology, but for example I just booked a ticket from TPA-HEL. I wanted to maximize routing with UA so I could have E+ and my double miles etc.

So if I went on united.com or any of the other websites it would tell me codeshares of flights through SAS as being the cheapest. The ticket looked like TPA-IAD-CPH-HEL then return. The price for the dates I wanted came to about $1400.

I figured I would try to do a multi-city booking so I could stay on UA aircraft as long as possible, since they do not fly to HEL. So I did a multi-city booking of TPA-FRA-HEL-FRA-TPA, basically a r/t with the connections I chose.

When I did this, the price of the ticket went down about $400 and also gave be better flight times and more options than with the SAS codeshare that kept popping up.

I'm not too familiar with who flies into ATH, but perhaps flying to BCN would be better? NYC-BCN is cheap at the moment I believe, then maybe a LCC to ATH from there?