To inform one's employer that one will be absent due to illness (real or feigned). The phrase originally referred to calling by phone, but can refer to any form of communication (such as email). That virus has totally decimated my staff—only two people are in the office today because the rest called in sick!

Is it called in sick or called out sick?

“Calling out sick” seems to be most common in New York, New Jersey, and Connecticut. But some people even say they "call off sick."

How do you say calling in sick?