The Overwatch Priority Pass is a new feature added in with the new update. With players jumbling themselves into teams at the last minute, competing for roles of DPS and Support, Blizzard has come up with a compensation for filling rolls called a Priority Pass.
Overwatch Priority Pass: How Does it Work?
You can earn Priority Passes by entering "flex queue," which will take you into whatever role is needed the most. You will get passes for a loss, but you can earn more for winning. You can hold up to 40 passes, though director Jeff Kaplan says that number may change.
If you want a role that has a longer queue, which Jeff Kaplan admits is probably the DPS role, you can spend a Priority Pass to get to that role faster.
The hope is that this system will make queueing faster for everyone, with more players moving into flex queues for Priority Passes so everyone gets into a full game faster. When the idea hits live, there will be more value for players actually using it in actual matches. Before that, there will be testing and bug checking so it may take some time before it hits live servers.