Covid-19 is the name given to the disease or we can say infection caused by Coronaviruses. As this new impact of coronaviruses started in the year 2019, the number 19 is attached to its name.
Covid-19 is also termed as SARS-CoV 2 disease because coronaviruses (CoV) cause SARS (Severe Acute Respiratory Syndrome) and the 2 in the name indicates the second outbreak, the earlier first outbreak was in the year 2002.
These coronaviruses primarily affect the respiratory system. however, there will be multi-organ failure and death if left untreated.
You can learn about coronaviruses from the answer to "What is Coronavirus? From where these viruses originated?"