absence due to illness; sick leave (can be used as a noun or as the verb phrase 'to take sick leave').
昨日は熱で病欠しました。
I took a sick day yesterday because I had a fever.
病欠の連絡は朝一番に会社へしてください。
Please notify the company first thing in the morning if you need to be absent due to illness.
彼は体調不良でたびたび病欠する。
He often takes sick leave because of poor health.