A backlog is every customer order that has been received as an order that has not yet fulfilled the customers request.
This type of work activity does not meet the criteria of value added work, mainly because a customer is not willing to pay for the product, service, activity or information. However, the product, service, activity or information although not considered value added is necessary to either protect the company or comply with regulatory requirements. Because of this it must be performed by the organization. This type of work is still considered wasteful.
Although business necessary work can not always be eliminated right away these activities should still be reduced or minimized as much as possible until they can be removed.
A bottleneck is the term used for any function, department, resource or facility whose needed capacity is less than the demand being placed upon it.
Bias is a term frequently used in forecasting and six sigma. Bias is the term used when a consistent deviation occurs from the mean/average. The deviation is always in one direction (either high deviation or low deviation). When forecasting a zero bias would represent a perfect forecast. In six sigma 0 deviation would represent absolutely no deviation from the established standard.