The definition of time between failure (TBF) is a measure of reliability that is used to assess the quality of a product or system. It is the average amount of time that passes between two consecutive failures of a system or product. TBF is used to measure the reliability of a system or product, and it is an important factor in determining the overall quality of a product or system. TBF is also used to measure the effectiveness of maintenance and repair activities. TBF is typically expressed in hours, days, or years, and it is used to compare the reliability of different products or systems. By understanding the TBF of a product or system, companies can make informed decisions about the quality of their products and systems.