It isn't like the rumble(no eliminations), it isn't like an ironman match (only the last fall counts), it isn't like the hardcore thing (way less people, no title changes), It isn't like an ROH scramble match, which is kind of what it is except instead of not being able to be won untill everyone is in the match it won't be necessarily won by a single fall, also there are no tags.
From the 'pedia:
Primarily associated with
Ring of Honor, a Scramble tag team match has one difference from the normal rules: when a wrestler goes out of the ring either of their own volition or by being forced out, a partner can come in as a replacement without being tagged in. This format is most commonly used in either four corner tags, or with teams of more than 2. The Scramble match can also be done as a six man scramble where anyone can tag in anyone.