From the World Health Organization
Question: What is a Coronavirus?
Answer: Coronaviruses (CoV) are a large family of viruses that cause illness ranging from the common cold to more severe diseases such as Middle East Respiratory Syndrome (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS-CoV).
Question: What is COVID-19?
Answer: Coronavirus disease (COVID-19) is a new strain that was discovered in 2019 and has not been previously identified in humans.
Question: How are coronaviruses transmitted?
Answer: Coronaviruses are zoonotic, meaning they are transmitted between animals and people. Detailed investigations found that SARS-CoV was transmitted from civet cats to humans and MERS-CoV from dromedary camels to humans. Several known coronaviruses are circulating in animals that have not yet infected humans.
This short video from the World Health Organization gives a basic description of COVID-19.