1. Any surface that moves up and down gently or is gently curving in one or more directions, particularly used to refer to water (waves, wavy) or land (hills, hilly), or any thing or any action that can be associated with this in a given context.
As a Noun
1. The large area of salty water that covers about three-quarters of the earths surface. English = sea.
2. A large area of salty water. English = sea, ocean.
3. A raised line of water on the surface of water, especially the sea, which is caused by the wind or by tides making the surface of the water rise and fall. English = wave
4. An area of land which is not level but undulates gently in all directions.
As a Verb or Adjective
1. To be changing level gently, up and down. English = undulate.
2. Of the surface of water, to undulate. English = (be) wavy.
3. Of an area of land, to undulate. English = (be) hilly.