According to a recent article on Port Technology’s website, because of the prevalence of the problem, the acronym UFO is now being used to describe Unidentified Floating Objects. This refers to floating sealife, general debris and shipping containers lost overboard, all of which pose a hazard to shipping.
Port Technology’s article states
Shipping containers that are being lost at sea are increasingly becoming the biggest lurking threat to containerships traversing the world’s busiest shipping routes.
Once shipping containers are lost, they do not immediately sink, and can then become dangerous hazards for passing containerships that have gotten so big pilots cannot see the lurking dangers in the water.