This Deans Connector Set connects two battery packs in parallel.

For example, you can make 2 x 2200mAh 11.1v 3S1P packs into a single 4400mAh 11.1v 3S2P pack.

Its an excellent and cheap way of buying larger lipos.
It means you dont need to upgrade your charger, or if you have a crash and damage a cell the loss is far less than losing an entire 3S2P pack.

Its the smarter way to run larger packs.