Many sites and companies aren’t trying to cram their keywords into content or hide any text on their site, but Google still attempts to warn web designers to avoid them. “Hidden text” or “keyword cramming/stuffing” refers to putting and writing keywords and terms solely for the purpose of search engine ranking, not for the customer or user to gain information from. This involves putting a keyword phrase multiple times in a webpage so often that the text and information on the page does not make sense due to the repetition of keyword phrases.
Much keyword stuffing is obvious to detect, and it may be difficult to know you are doing it moreso than informing your readers. In order to test this, try reading your written text out loud. If it sounds unnatural. If it makes sense to you and sounds good, it should be good enough to use.
Keyword cramming can be an issues because users who are looking for certain keywords want to see them on your page in a way they can use them and find information. They do not want to be directed to your site simply because of hidden text in your footer. This generally produces a frustrating experience for users that search through Google, which is why Google has a strong opinion on it.
Hidden text and keyword stuffing is common on WordPress sites, so if you receive a warming for hidden text, your first thing to do is check to see if you have been hacked and if so, upgrade so that you can cleanup the issue. Google also advises you to document this clean up process, including what you found, how you fixed it, and the dates in which you did so. Also include why it happened, and explain why you don’t think it will happen again.