Plural. Jewish/Yiddish slang for a person's intestines or digestive system.
"I remember that when they announced from the radio the explosion of the first atomic bomb, he said aloud, 'maybe that would do the job.' But all catharses were in vain for that man: his KISHKAS were gripped by the iron hand of outrage and frustration. Among his other misfortunes, I was his wife's favourite"
- Portnoy, talking about his father's constipation. From 'Portnoy's Complaint', by Philip Roth