It is the database for Windows search indexing indeed. You can either safely:
Rebuild it. Do that by either searching Indexing options or launching them through Control Panel after showing all icons. Then go to Advanced and click Rebuild. Doing that might reduce its size heavily. It will grow later though.
Disable indexing or choose less locations to index. Again go to Indexing options but click Modify this time. Choose only folders that have files that need to be found quickly. Or don't choose anything if you use app like Everything which is generally faster and less space-consuming. Rebuild index after that to make sure it applies the new settings.
Disable Windows Search service temporarily and then delete the file manually. First two options are much more recommended though.
