What is the meaning of throw in?

verb

• Add as an extra or as a gratuity.
• Give up in the face of defeat of lacking hope; admit defeat.
  • usage: "In the second round, the challenger gave up"
  • synonyms: drop out, give up, fall by the wayside, drop by the wayside, throw in the towel, quit, chuck up the sponge
• To insert between other elements.
  • usage: "She interjected clever remarks"
  • synonyms: interject, come in, interpose, put in, inject