Plastic particles less than 5 millimetres in diameter, including nano-sized particles. Source: United Nations Environment Assembly resolution 2/11, “Marine litter and microplastics”, para. 1.* *This term is included in the glossary of key terms prepared for the work of the intergovernmental negotiating committee to develop an international legally binding instrument on plastic pollution, including in the marine environment, under the category 'Terms used in Environment Assembly resolution 5/14 that have definitions adopted or endorsed by an intergovernmental process'. See UNEP/PP/INC.1/6.