Google uses the description in the SERPs

The SERPs or Search Engine Result Pages are Google's response to a search, showing potentially interesting result for the searched keyword.

When you type something in google it will show you a SERP with potential results.

The results shown come from a mix of several things, but can be controlled by the meta elements on your webpage.

SERPs Main elements

Although the SERPs from different search engines have many and different features, following 2 elements will be standard for most search engines including Google.

Organic items

The results in the organic items are links and pieces of content that are shown because they have a high likelihood of being relevant to the search user. For example, these entries might answer the user’s question, be an example of what the user is searching for, or may cover a related topic. Here, the search engine’s job is selectively choosing results that have the greatest chance of making the user satisfied—and therefore more likely to use the search engine again.

Advertising

The advertisement items are ads that are displayed because a company, individual, or organization has paid for their appearance. This is one of the primary ways that search engines like Google make money. Millions of people browse SERPs each day, so SERPs function much like a newspaper or a magazine; advertisers can pay money to get readers’ attention. These ads are served dynamically, rather than statically, meaning the content can change throughout the day and in response to different users.

Control your entries in the search result

If your website has a title or meta tag, it is likely that Google will use the text in the SERPs

Example

<title>Google</title>
<meta name="description" content="Learn how to write a quality meta description tag that may be displayed for your page in Google Search results by following these best practices.">   

The end result might be something like this screenshot

Omitting the title or description tag will result in Google rewriting the description

In several cases, Google will decide the rewrite your description, and or title, regardless of wether the webpage provide these details

How to fix the issue?

The rules that Google uses to rewrite the title and or description are unknown.

If you find that most of the description or titles have been rewritten in the serps, consider rewriting them to match the Google description

If the description is too long, rewrite the title and description in a more succint form.