Are you unintentionally spamming search engines

Are you sure that your website is free of hidden text? There are many ways to create hidden text unintentionally. By checking your web pages, you make sure that you won't be penalized for something you did not intend to do.
Why is hidden text a problem?

Google doesn't like hidden text and hidden links at all. Here's the official text from Google's guidelines:
Hiding text or links in your content can cause your site to be perceived as untrustworthy since it presents information to search engines differently than to visitors. [...]
Hidden links are links that are intended to be crawled by Googlebot, but are unreadable to humans. [...]
If your site is perceived to contain hidden text and links that are deceptive in intent, your site may be removed from the Google index, and will not appear in search results pages.

How can you hide text on your web pages?

There are many methods that allow you to hide text on your web pages:
using white text on a white background

including text behind an image

using CSS to hide text

setting the font size to 0 or a negative value

If you wittingly use some of these methods on your web pages, you should make sure that you remove them as soon as possible.

Are you sure that you don't use hidden text unintentionally?

There are a few legitimate reasons to hide text on a web page. For example, you could use CSS to replace a text link with a more pretty graphical button.
Many content management systems (CMS) use the CSS display:none technique to create drop-down menus or other expandable web page elements. Although these elements are not designed to mislead web surfers, search engines might interpret the hidden texts as a spamming attempt.
Another way to create hidden text is to provide enhancements for visually impaired people. If a lot of text on your website can only be seen by screen reader software and not by regular web surfers then some search engines might misinterpret this as spamming.

How can Google discover hidden text on your web pages?

It's relatively easy for Google to find out if your website contains hidden text. However, it's difficult to find out whether a page uses hidden text for legitimate reasons or not.
Google's spam filters might be applied to your website if the following happens:
The hidden content contains keywords that are unrelated to the rest of your content.

The hidden text contains too many keywords. If a large part of your web page content is hidden, your website might look suspicious.

You overuse "legitimate" ways to hide text on your web pages. This might flag your site for a human review.

One of your competitors reports your site to Google because he detected spam techniques on your site.

Google won't ban your site if you use hidden text in a way that appears to be legitimate. They try to detect intent. Don't try to cheat search engines. If you use ethical search engine optimization methods then you don't risk getting banned from the search results.