Extraterrestrial Biological Entity - the one in the video was kept inside a Faraday cage because of it's ability to pass through solid walls. It needed to use electromagnetic energy to do that.

Sorry, here you go!

ETs - Extraterrestrials
NHI - Non-Human Intelligence
EBEs - Extraterrestrial Biological Entities
UFOs - Unidentified Flying Objects
UAPs - Unidentified Aerial (or Anomalous) Phenomena
USOs - Unidentified Submerged Objects
ARVs - Alien Reproduction Vehicles
OVNI

There are more that have been used throughout the years by military but I couldn't remember off the top of my head.