Final answer:
Fossil fuel refers to an energy source buried in the ground, such as coal, petroleum, or natural gas. Fossil fuels are ancient solar energy captured in living matter and stored underground over millions of years.
Step-by-step explanation:
Fossil fuel refers to an energy source buried in the ground, in the form of coal (solid), petroleum (liquid), or natural gas (gaseous). Fossil fuels represent ancient solar energy captured in living matter, processed and stored underground over millions of years.