A "T" rating indicates the amount of time (usually hours) it takes the temperature on the non-fire side of a fire-rated assembly to exceed 325 degrees Fahrenhiet above ambient temperature.

An "F" rating indicates the amount of time (hours) that a fire-resistive barrier can withstand fire before allowing flame to pass through an opening.

An "L" rating denotes the amount of air leakage (cubic feet per minute) through a penetration