Motu Proprio - (Latin) on his own initiative
Typical for me to be asleep at the wheel during the most cataclysmic event in the Church in the last 45 years. I've been wrapped up with serious family affairs and with making sure my children are having fun in the pool as opposed to furiously typing into this PC.
Anyway, the Pope, on his own initiative, issued a document which allows any Roman Catholic priest to offer the Tridentine (Latin) Mass. These Masses had previously only been allowed per special permission, aka "indult."
Here's a few articles to flesh out this issue. One from Boston and one from Atlanta. (Hat tip to Cafetria is Closed for the Atlanta article.)