Coronaviruses are a large family of viruses known to cause diseases in mammals and birds. In humans, these viruses cause (typically) mild to moderate respiratory infections, like the common cold. Two of the newer coronaviruses, MERS and SARS, have been known to cause severe illness and can be fatal.
Most coronaviruses infect animals and rarely evolve to infect and spread between humans.
The most recent coronavirus to make the news is the 2019 Novel Coronavirus, or 2019-nCoV. It has caused an outbreak of respiratory illness that was first detected in Wuhan, China. Early patients were linked to a large seafood and animal market, but more recent ones reported no exposure to animal markets which indicated person-to-person spread, though it is unclear how easily.
Novel Coronavirus 2019, Wuhan, China. (2020, January 28). Retrieved January 31, 2020, from https://www.cdc.gov/coronavirus/2019-nCoV/index.html