What is the meaning of Whortleberry?

Any of several shrubs belonging to the genus Vaccinium:

Vaccinium myrtillus (bilberry or blue whortleberry);

Vaccinium vitis-idaea (lingonberry or red whortleberry);

Vaccinium uliginosum (bog whortleberry or bilberry).

A berry of one of these shrubs.

Source: wiktionary.org