The abbreviations 'OT' and 'ST' on the Contractor's Payroll Form refer to 'Overtime' and 'Straight Time', respectively. Overtime hours are hours worked in excess of the regular workday or workweek, while straight time refers to regular hours worked. Overtime hours are typically paid at a rate of one and a half times the employee's regular rate of pay, while straight time hours are paid at the employee's regular rate of pay.