What is a Meta Description?
A meta description is an HTML element that describes and summarizes the contents of your page for the benefit of users and search engines such as Google often display the meta description in search results.

Example of meta description in the page :

   <meta name="description" content="This is an example of a meta description. 
This will often show up in search results."/>
Meta Description
Meta description length :

Meta descriptions can be any length, but Google generally truncates snippets to ~155–160 characters. It's best to keep meta descriptions long enough that they're sufficiently descriptive, so we recommend descriptions between 50–160 characters. Keep in mind that the "optimal" length will vary depending on the situation, and your primary goal should be to provide value and drive clicks.

Importance the Meta Descriptions in SEO :

Since meta descriptions appear with your title and URL on the results pages, they have the power to help or hurt your results’ click through rates. Research has shown that having the keyword in the body of the meta description is a relevancy signal for search engines that can help your rankings.

To encourage clicks and bring visitors from search to your website, do the following with your descriptions :

1. Aim for about 1-2 sentences (140-160 characters) long

2. Include your target keyword

3. Avoid duplicate meta descriptions

4. Make it meaningful and descriptive, matching your content

5. Double check how it looks with a SERP view generator tool