Despite its relatively broad, but highly discontinuous range, White-bellied Dacnis is one of the most poorly known and relatively infrequently seen bird species in South America. Its main range is in western Amazonia, where it occurs in southwest Venezuela south and west to northeast Peru, but there are also a handful of records in central and east Amazonian Brazil, both north and south of the Amazon. It has been recorded in both seasonally flooded and terra firme forests, and is usually observed within mixed-species canopy flocks. Seen well, males are much darker blue than those of any other species of Dacnis, with a black mask and yellow irides, black markings on the wings, and a large white belly and ventral region. Females are less distinctive, being greenish above, with a grayish-white throat and greenish-yellow underparts.
Its scientific name, Dacnis albiventris, has Greek and Latin origins. The genus name Dacnis comes from the Greek word "Daknis", which is an unspecified type of bird from Egypt (Jobling 2010). The specific epithet of albiventris comes from Latin word albus meaning "white", and ventris meaning "venter", or belly (Jobling 2010). In Spanish, the common name is Dacnis Ventriblanco (Hilty 2011, de Juana et al. 2012); in Portuguese it is Saí-de-Barriga-Branca (Sick 1993, CBRO 2010). Collectively, the scientific and common names of this species refers to the male's distinctive white belly.