What is "cortober"

Cortober is a townland in County Roscommon, Ireland. It is located across the bridge from the town of Carrick-on-Shannon on the right bank of the River Shannon. It is bounded on the north by the parish of Tumna and River Shannon, on the east by the River Shannon, on the south by the townland of Cordrehead and Killukin and on the west by Mullaghmore.