is a specific kind of: heath.

is a broader term that covers: briar, brier, Erica arborea, tree heath | Erica carnea, spring heath, winter heath | bell heather, Erica cinerea, fine-leaved heath, heather bell | bell heather, cross-leaved heath, Erica tetralix | Cornish heath, Erica vagans | Erica lusitanica, Portuguese heath, Spanish heath | Erica perspicua, Prince-of-Wales'-heath, Prince of Wales heath.

is a member of: genus Erica.