It is an update rule: Wij = f(Wij, xi, xj) The weight of the connection between nodes i and j is modified by a function over the activations or inputs of node

It is an update rule: Wij = f(Wij, xi, xj) The weight of the connection between nodes i and j is modified by a function over the activations or inputs of node i and j. The are many variants of back propagation too. Regardless, yes it would be used within a network model such as a Hopfield network.