PPC expert witness: A PPC expert witness (Pay per Click expert witness) will conduct technical analysis in order to provide an opinion concerning pay-per-click (PPC) advertising, which is the a online advertising model in which advertisers' ads are associated with certain words on search engines, the ads can appear when a person searches with those words, and the advertiser pays the search engine when the person clicks on the ad. 

A PPC expert witness is also know as a pay-per-click expert witness or a search engine marketing expert witness (aka, SEM expert witness). 

There are a wide range of analysis that a PPC expert witness can provide, including revenue, revenue harm, trademark infringement, and advertising traffic, among many others.​                                                                                                                                                      (4 Sep 2017)