Patent Validity expert witness: A patent validity expert witness provides technical analysis in order to provide an opinion concerning patent validity, which means whether or not the claims of a patent are valid.​ [1]). 

There are a variety of issues that patent validity expert witness in the information technology area might analyze relating to whether or not a patent claim is valid, include a claim not being novel due to prior art, a claim not being novel due to  being known in the industry, or a claim not being an inventive innovation, among many others.

1. http://www.priorartsearch.com/validity.htm                                                                                                                       (as of 2021)