Invasion (Upstairs)
WordNet
noun
(1) The act of invading; the act of an army that invades for conquest or plunder
(2) (pathology) the spread of pathogenic microorganisms or malignant cells to new sites in the body
"The tumor's invasion of surrounding structures"
(3) Any entry into an area not previously occupied
"An invasion of tourists"
"An invasion of locusts"