The name nabla for the upside-down delta ∇ (aka an atled) comes from its shape: it is vaguely reminiscent of a harp, which is "nevel" in Hebrew. V and B being interchangeable under some western Semitic circumstances, the name nabla was given to the symbol.

∇ is merely a differential operator producing the partial derivatives in each variable. So for f:Rn→X,

∇f = (∂/∂x1,...,∂/∂xn)f