It is usually in music an abbreviation. HWV is Handel's Index or Catalogue of Works (German: Handel Werke Verseichnis).
HWV . Acronym for Handel Werke Verseichnis, in German, Catalogue of Handel's Works. Like BWV, Bach Werkw Verseichnis and RV, Vivaldi's Ryom Catalogue do not have a chronological but thematic order.