What does "surf" mean?

Surf: The swell of the sea which breaks upon the shore, esp. upon a sloping beach. Surf bird (Zoöl.), a ploverlike bird of the genus Aphriza, allied to the turnstone. -- Surf clam (Zoöl.), a large clam living on the open coast, especially Mactra, or Spisula, solidissima. See Mactra. -- Surf duck (Zoöl.), any one of several species of sea ducks of the genus Oidemia, especially O. percpicillata; -- called also surf scoter. See the Note under Scoter. -- Surf fish (Zoöl.), any one of numerous species of California embiotocoid fishes. See Embiotocoid. -- Surf smelt. (Zoöl.) See Smelt. -- Surf whiting. (Zoöl.) See under Whiting.