Mouse - Kensington Technology Group Compatible Computer Devices

Description extracted from Wikipedia:

thumb|Rightmost opening on the side of this laptop computer is a Kensington Security Slot A Kensington Security Slot (also called a K-Slot or Kensington lock ) is part of an anti-theft system designed in the early 1990s and patented by Kryptonite in 1999-2000, assigned to Schlage in 2002, and since 2005 owned and marketed by Kensington Computer Products Group, a division of ACCO Brands.