The US Congress passed a bill in 2006, The Marine Debris Research, Prevention, and Reduction Act, to create a program to address the marine debris pollution. One of the requirements in the bill was for NOAA (National Oceanic and Atmospheric Administration) and the . Coast Guard, to promulgate a definition of marine debris for the purposes of the Act. Thus, USCG and NOAA drafted and published a definition of marine debris in September 2009. The definition is this: “Any persistent solid material that is manufactured or processed and directly or indirectly, intentionally or unintentionally, disposed of or abandoned into the marine environment or the Great Lakes.” Marine debris can come in many forms, from a plastic soda bottle to a derelict vessel. Types and components of marine debris include plastics, glass, metal, Styrofoam, rubber, derelict fishing gear, and derelict vessels.
Keter-class Objects are broadly defined as "inimical threats to all of humanity", and are listed along with Humanoids and Jokes as concepts that are difficult to write because the process of coming up with something that is broad-reaching enough to threaten all of humanity while allowing the Foundation to maintain the veil of secrecy and being an interesting read is surprisingly difficult. While a planet-sized monster that can swallow the earth in one gulp might certainly be classified as a Keter-class entity, it would be almost impossible to write it in such a way as to be plausible (within the Foundation's literary framework) and interesting.