Incognito Mode is a feature that can be accessed by a variety of browsers, including Google Chrome and Firefox, that opens a new browser which does not save the browsing history of that session. This mode of browsing is also sometimes referred to as Private Browsing.
For marketers, Incognito Mode means that cookies and site data are not saved across browsing sessions. Because these data are important for targeted advertising as well as tracking traffic to and from a website, the use of Incognito Mode means that marketers have far less information about the browsing habits of web users than if they were not to engage the mode.