"These implementations" means the copyrightable works that implement the WebM codecs distributed by Google as part of the WebM Project.
Google hereby grants to you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable (except as stated in this section) patent license to make, have made, use, offer to sell, sell, import, transfer, and otherwise run, modify and propagate the contents of these implementations of WebM, where such license applies only to those patent claims, both currently owned by Google and acquired in the future, licensable by Google that are necessarily infringed by these implementations of WebM. This grant does not include claims that would be infringed only as a consequence of further modification of these implementations. If you or your agent or exclusive licensee institute or order or agree to the institution of patent litigation or any other patent enforcement activity against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that any of these implementations of WebM or any code incorporated within any of these implementations of WebM constitutes direct or contributory patent infringement, or inducement of patent infringement, then any patent rights granted to you under this License for these implementations of WebM shall terminate as of the date such litigation is filed.
See also: Software License