Grove Music online is our primary music eReference tool, and it includes a lot of information on world music. Keep searches simple, and look for the broader categories that discuss your topic.
These are good places to check if you want a short definition or summary of a musical concept, instrument, or musician. Tip: Use the "Search within title/publication" box so that you don't search the larger database.
A great print encyclopedia on world music, where you can find substantial essays on the traditional music of a nation you are researching. Expect them to be longer than an article but shorter than a book.
Multi-volume encyclopedia that focuses on global popular music. The first two volumes give a breakdown of the industry and instrumental areas. The rest of the set contains 2 volumes on each continent, one with essays broken down by nation/region/city, and the other by musical genre.