This is to make a wireless network connection work better without
spending $100.00 or more. An "Omni" antenna is an all-direction
antenna, the 802.11 it references is the specification for the
computer wireless networks.
Usually an omni-directional antenna like this would be attached to the
base station or access point, and a directional antenna (like the
pringles can one you may have come across) would be attached to the
computer and pointed at the omni. I have personally setup 5+ mile
links with a setup like this (using commercial antennas, not homemade
ones.) Others have gotten connections out to 30-40 miles with two
directional antennas pointed at each other.