Those of you who do a lot of editing with Japanese and Korean music should be pretty familiar with the term “mini album” (ミニアルバム). I’ve always understood it to simply be a marketing term used in their countries’ music industries that is our equivalent to an EP (they almost never use the term EP). Wikipedia seems to agree with me as the wiki for Mini-LP has a note at the top saying, “‘Mini-album’ redirects here. For mini albums released in Japan and South Korea, see Extended play.”
And moreover, for Japanese, EP has been the classic 45 rpm 7 inch vinyl singles.
I used to classify mini albums as MB EP, but later I moved them to album, considering mini album as a missing RG attribute but that is not really missing, I don’t feel strongly about putting them apart from albums, like I think maxi singles are very good with all singles.
In Korea mini-albums often get re-issued with extra tracks, and can end up having more of a “regular” album length. Here is a mini-album that has 13 tracks and is 36 minutes long: