The Original Release Date is the date the album was first made available for sell anywhere in the world and in any format.
For brand new albums, The Original Release Date would be the same as the Street Date (Learn about the Street Date here).
It's very important that if your album has ever been sold in the past, that you submit the real Original Release Date for that album. The music stores frown on providing an incorrect Original Release Date for albums that have already been released before, and they have sometimes completely removed albums if the date was not accurate (Especially for every old albums that have recently been digitized for modern music stores). They utilize some 3rd party services that keep a record of historical albums and if they find it is incorrect, it can create problems for your album.
IMPORTANT: If the album is a remastered version of a previously released album, you would submit the Original Release Date of the original album.