INVISIBLE DIVs / ZERO-WIDTH/ HEIGHT DIVs

In HTML, the span and div elements are used where the document cannot be semantically described by other HTML elements. For example, the paragraph tag (P), header tag (h1) all describes a function according to the type of data it contains. But in span and div there is no logical grouping. There are ways you can hide contents inside div and spam the search engines. Div tags are superficial layers and when you hide content behind the div tag it will be difficult for the users to see it. For search engines however it is part of the html document and they can see and read it. Many users were trying these tactics to hide content behind the div tags so that users cannot see but the search engines can see it.

Also we have hidden divs, where you can literally hide the contents inside divs and search engines can see it but users do not. But back in 2005, an update called the "Google Jagger update" literally killed the usage of hidden divs and from that time, there has been speculation that Google is not reading hidden divs. Also hidden divs can be directly defined from the CSS. A simple example:
#mainav {position: absolute; visibility: hidden ;}.

It's evident in the "Jagger update" Google only killed the usage of divs without penalizing the sites that uses them. This is because there are valid reasons to use hidden divs in CSS or on your html page. A simple rule of thumb, do what is best for your users, if the users can see it and enjoy your webpage and the information you have and what you are doing is right. Search engines will pick and appreciate the right stuff you do.