What is Bait and Switch?
In SEO, the "bait and switch" is a technique that involves optimizing a webpage for certain popular keywords to achieve high rankings and then switching back to the targeted content.
More precisely, when the desired ranking is achieved through popular keywords, the site owner changes the content of the page to what they actually want to promote. The motive behind it is to mislead search engines and users to drive traffic to the site.
For example, a webpage ranks well for having content about a trending topic or issue by utilizing the trending keywords. Then, after achieving this target, the content is replaced with content on an entirely different topic that the site owner actually wants to promote.
This practice is against Google's Webmaster Guidelines, and the websites being caught using such tactics are liable to be penalized by Google.