The Mass Effect story of Shepard and his/her crew ended back in April 2013 with the arrival of the last DLC pack, but this universe isn't done yet.
Mass Effect Andromeda is set a long time in the future and very far away from the events we're familar with. There's a whole new crew and new stomping grounds in the Andromeda Galaxy, in case you thought the title was meaningless.
You'll play as a lady or a dude, in this case one of a pair of siblings- which should mean the other character will remain as an NPC in a change for the series. You're off out looking for a new place for the human race to continue their spread across the Universe, and plenty of talking and shooting and some romancing will get in the way of that.
Now we might know when that adventure is kicking off with a new leak. Destructoid spotted an art book for the game called The Art of Mass Effect Andromeda on Amazon. This no doubt very glossy publication is said to release on the 21st of March 2017, and claims to be arriving on the same day as the game.
This isn't a sure thing but does tie into the early 2017 release date suggested by EA and BioWare and is roughly similar to the date for the most recent entries in the series. It's expected we'll hear more on the project on the 7th of November, because that's N7 day- a totally randomly made up celebration of all things Mass Effect.