Simply put, a cash credit line is the amount of money made available for cash back (think ATM or grocery store transactions where you can request money back). Credit card companies will reserve a portion of your available credit limit to be used as a cash credit line (sometimes referred to as a cash access line) because they understand you may be in a pinch and need to leverage your card more like a debit card. But beware: the fees and interest rates associated for using your card like a debit card are higher than the rates you pay on other purchases. Read the fine print.