OpenH264 is an implementation of the H.264 video codec.
It was released as open source by Cisco, who have paid royalties for it to the MPEG-LA.
To avoid royalty payments, the OpenH264 implementation can only be used in its binary form and only if downloaded dynamically by an application and not pre-packaged in advance.
The idea behind the OpenH264 initiative is that by making it freely available, it gives H.264 more of a chance to become the mandatory to implement video codec in WebRTC.
Mozilla announced support for the OpenH264 and has integrated it into their latest nightly builds of Firefox as an additional video codec.