Unity or Identity Matrix

A square matrix whose main diagonal elements are all unity and the other elements are zero is called a unity or identity matrix.

Unpaid Cheque

This is a cheque, which is returned ‘unpaid’ (bounced) by the drawee bank.

Universal Set

It is the set which includes all the sets that exists.

Uptime

Amount of time your web server would be completely accessible and not interrupted by technical errors. It is calculated in terms of percentage. An uptime of 99% or more is considered ideal.