What is the meaning of undulate?

verb

• Stir up (water) so as to form ripples.
  • synonyms: ripple, ruffle, riffle, cockle
• Occur in soft rounded shapes.
  • usage: "The hills rolled past"
  • synonyms: roll
• Move in a wavy pattern or with a rising and falling motion.
  • usage: "The curtains undulated"; "the waves rolled towards the beach"
  • synonyms: roll, flap, wave
• Increase and decrease in volume or pitch, as if in waves.
  • usage: "The singer's voice undulated"

adjective

• Having a wavy margin and rippled surface. .