This stands for Conference of the Parties (states) to the UNFCCC. It is where decisions are made about climate change under the UNFCCC. All states that are members of the UNFCCC are represented at the COP. It meets most years. The last COP (COP 25) was held in Madrid, Spain in December 2019, and the next COP (COP 26) will take place in Glasgow, United Kingdom, in November 2021.
You can find out more about COP 26 at www.ukcop26.org