It usually comes down to what the band says it is, and/or what is counted as an album or an EP. Obviously, genre and length sometimes go hand-in-hand. A powerviolence/grindcore EP may be 10 songs long.
I guess you could make the argument between 7/8 songs which is an EP, or if it's a mini album or album. Alice in Chains' Jar of Flies is considered an EP, I think. Though I'm pretty sure 8 songs would be considered an album by today's standards. After the Burial's In Dreams is considered an album, 8 songs long.
I'd probably say a mini-album is a more cohesive EP, but is cheaper than an LP.