The new pledge, officially named the "Open Patent Non-Assertion Pledge" (or OPN Pledge for short), indicates that unless otherwise attacked by another creator of open-source software, Google will not use its patents against any other entity. The entire pledge runs a few paragraphs (and can be seen at the source link below), but the idea is that Google wants to be able to hold patents to protect itself (and software) from attack while agreeing to not attack themselves. A small excerpt from the pledge reads:

It is Google’s intent that the Pledge be legally binding, irrevocable (except as otherwise provided under “Defensive Termination” below) and enforceable against Google and entities controlled by Google, and their successors and assigns.

Meaning that not only does the pledge apply to Google's own operations, but also those of any company owned or operated by it -- such as Motorola, presumably -- as well as any company that buys or sells patents with Google. The pledge states that any company receiving patents from Google must agree to the terms of the pledge in their own use, and also have similar requirements if it were to ever transfer the patents again to a third entity.

It is worth noting that the OPN Pledge only applies to other entities that are also making open-source software, and makes no mention that Google's patents couldn't be used offensively against one making closed-source software. And while Motorola presumably falls under the category of "entities controlled by Google", because it is technically being run as an independent company we're unsure on how this pledge affects it.

Reiterating that it believes that open internet and open software systems are the best choice for everyone, Google is hoping that the OPN Pledge "will serve as a model for the industry". It also notes the devotion to open-source software by other entities like IBM and Red Hat, which are said to be examples for what the OPN Pledge was built on.

Source: Google Open Source Blog; OPN Pledge