Lignites are a type of soft brown coal that is commonly used in power plants to generate electricity. However, there are several synonyms that refer to lignites or coal of a similar grade, including sub-bituminous coal, brown coal, and low-grade coal. These terms are often used interchangeably, depending on regional variations in usage and geological context. Other synonyms for lignites include sapropelic coal, boghead coal, and "brun coal" in some European languages. While lignites are not as energy-dense as other types of coal, such as anthracite or bituminous coal, they are widely available and relatively inexpensive, making them an important source of fuel for many countries around the world.