A MultiViews search is where the server does an implicit filename pattern match, and choose from amongst the results.

For example, if you have a file called configuration.php (or other extension) in root folder and you set up a rule in your htaccess for a virtual folder called configuration/ then you'll have a problem with your rule because the server will choose configuration.php automatically (if MultiViews is enabled, which is the case most of the time).

A MultiViews search is enabled by the MultiViews Options. If the server receives a request for /some/dir/foo and /some/dir/foo does not exist, then the server reads the directory looking for all files named foo.*, and effectively fakes up a type map which names all those files, assigning them the same media types and content-encodings it would have if the client had asked for one of them by name. It then chooses the best match to the client's requirements, and returns that document.

The MultiViewsMatch directive configures whether Apache will consider files that do not have content negotiation meta-information assigned to them when choosing files.