The upper specification limit as specified by the customer, engineering or management. This number represents the maximum acceptable/allowable value for a characteristic being measured with continuous data.
Specifications are commonly expressed in the form: the target plus or minus the allowable margin of error.
Thus the specifications for the weight of a box of cereal may be (15 +/- 0.5) oz., which means the actual weight of the box may vary between 14.5 and 15.5 oz. and still be acceptable. Here 14.5 is the lower and 15.5 the upper specification limit.
In some cases the margin of error may be expressed in terms of the process variation, or sigma: (15 +/- 1?) indicates that the weight can vary to within 1 sigma of the target (15 oz.) in either direction. The upper specification in this case is (15 + 1?) while (15 - 1?) is the lower specification.