What is the meaning of invasion?

noun

• The act of invading; the act of an army that invades for conquest or plunder.
• Any entry into an area not previously occupied.
  • usage: "an invasion of tourists"; "an invasion of locusts"
  • synonyms: encroachment, intrusion
• Pathology) the spread of pathogenic microorganisms or malignant cells to new sites in the body. (
  • usage: "the tumor's invasion of surrounding structures"