Grove Music Online (GMO) is an "online encyclopedia" that includes the full text of The New Grove Dictionary of Music and Musicians, The New Grove Dictionary of Opera, and The New Grove Dictionary of Jazz. According to their website, "Grove Music Online is updated annually to ensure it remains the most up to date music reference work on the Internet."

The results of any search in GMO will be listed by relevance, in other words, the frequency in which the search terms appear in each article. The annotation of "Jazz" or "Opera" identifies articles from the New Grove Dictionary of Jazz and the New Grove Dictionary of Opera respectively.
GMO also uses color to distinguish the source of the article.

Blue = Dictionary of Music & Musicians  Red = Dictionary of Opera  Purple = Dictionary of Jazz

Definitions of musical terms
Descriptions of historical periods
Discussion of a composer's life, works and style which concludes with a list of works and bibliography.
Articles on jazz artists usually contain a discography (list of recordings).
Articles on operas include composer(s), librettist(s), roles, plot synopsis, etc.