IP in this context stands for Intellectual Property.
Intellectual property is something unique that has been physically created. An idea alone is not intellectual property. However, a produced game does count.
The IP is anything that is subject to copyright, patents and trademarks. Developers/publishers get some types of protection automatically. Others require registering.
The following gives some examples of items that are considered IP:
- The plot to a video game
- Characters, including names and appearances
- The overall look and feel
- Sound and video
- The name of the game
- A game's engine
Often, IP and franchise/brand are interchangeable. For example, Nintendo may refer to Mario as IP, a franchise or a brand. I believe that is the case with the quote in the question.
US Policies on IP
UK Government Article
As a side note, IP is also used in gaming when referring to someone's IP address or the Internet Protocol.