What is the meaning of hunkered down?

verb

• Sit on one's heels.
  • usage: "In some cultures, the women give birth while squatting"; "The children hunkered down to protect themselves from the sandstorm"
  • synonyms: squat, crouch, scrunch, scrunch up, hunker, hunker down
• Take shelter.
  • usage: "During the sandstorm, they hunkered down in a small hut"
  • synonyms: hunker down
• Hold stubbornly to a position.
  • usage: "The wife hunkered down and the husband's resistance began to break down"
  • synonyms: hunker down