Thermocline is a term commonly used in the context of aquatic environments, referring to the layer of water in which the temperature gradient is steep. There are several synonyms for this term which include halocline, the layer in which there is a sharp change in salinity; chemocline, the layer in which there is a sharp change in chemical properties and pycnocline, which is the layer in which the density gradient is steep. Additionally, there is also the metalimnion, which is the transitional region between the epilimnion and hypolimnion in a stratified lake. Understanding these synonyms is essential for better comprehension of aquatic sciences.