Nabla symbol
The nabla is a triangular symbol resembling an inverted Greek delta: ∇ {\displaystyle \nabla } or ∇. The name comes, by reason of the symbol's shape, from the Hellenistic Greek word νάβλα for a Phoenician harp, and was suggested by the encyclopedist William Robertson Smith in an 1870 letter to Peter Guthrie Tait.