The fromfilename plugin helps to tag albums that are missing tags altogether but where the filenames contain useful information like the artist and title.
When you attempt to import a track that's missing a title, this plugin will look at the track's filename and guess its track number, title, and artist. These will be used to search in MusicBrainz and match track ordering.
To use the fromfilename plugin, enable it in your configuration (see using-plugins).