incursion

noun

1. A military action consisting of armed forces of one geopolitical entity entering territory controlled by another such entity, generally with the objective of destruction, plunder, or bodily harm rather than an intent to conquer territory or alter the established government; contrast invasion in its narrow sense.
2. An aggressive movement into somewhere; an invasion in the general sense.

   “Fascinating though the journey is to the traveller, for many years this section of the line was a source of considerable anxiety to the maintenance engineers, and on more than one occasion landslips and incursions of the sea resulted in the railway being closed for several days.”

3. (Australia)A function hosted within an educational institution, especially by or for students, for recreation, research, education or a display of works.