“% Committed Bytes In Use is the ratio of Memory\Committed Bytes to the Memory\Commit Limit. If the paging file is enlarged, the commit limit increases, and the ratio is reduced).
The commit limit is determined by the size of the paging file. Committed Memory is the number of bytes that have been allocated by processes, and to which the operating system has committed a RAM page frame or a page slot in the page file (or both). Windows allocates memory for processes in two stages. In the first stage, a series of memory addresses is reserved for a process.

Committed memory is the physical memory in use for which space has been reserved in the paging file should it need to be written to disk.