Review by Francisco Taveira Pinto (June 2013)
Actual: "Process affecting wave propagation, by which energy is radiated normal to the direction of wave propagation into the lee of an island or breakwater"
Another: "Process by which energy is transmitted laterally along a wave crest. Propagation of waves into the sheltered region behind a barrier such a breakwater" - The Rock Manual, CUR, CETMEF, CIRIA.
My suggestion: "Process by which energy of a wave is transmitted, radiated and dissipated laterally when reaching an obstacle such a breakwater and propagates into its sheltered region."; an image would help to understand.