When your business publishes a webpage, you want people to see it. If by art or luck, you got your webpage near the front page of a Google search, users still have to choose your page over all the others they find there. They will pick your page - or not - based on the title and the mini description underneath. These descriptions represent Google's best attempt to tell people what this page is about and how it can help them.
Where does Google get these descriptions
If your page came up because you paid for a google ad, you have more control of the resulting text. For organic ads, it's not entirely up to you. About 30% of the time, Google will use your "description" meta tag. Meta tags are HTML tags that don't show up on the screen, but are used in various ways. In many cases, Google will just use the content of this description tag to tell Googlers what this page is about. But not always.
Google rewrites descriptions more often than not. For example, I tried a search "lawn dandelion" and found a result from lawnstarter.com titled "The Top Benefits of Dandelions in Your Yard." Underneath was the description:
"Dandelions are very good for the beneficial insects and pollinators in your yard,” she said. “And they have tap roots that accumulate nutrients ..".
This hardly looks like what anyone would write in a meta tag. Especially since Google just picked up a quote out of context and even cut it off in the middle. The description that this webpage publisher wrote reads:
"The dandelion, that yellow flower that turns into a puffable white ball may be a weed to some, but there are many benefits of having them in your yard.."Read More.
What is even more surprising is that Google will change the description depending on the search. For example, if you search "lawn dandelion roots" instead of "lawn dandelion", you get the description:
"Dandelion roots may be a real pain to remove from your lawn, but when you see how good they are for you, you just might want to keep them ..."
for the same exact webpage. In this case we see that Google tried to pick up the gist of what the Googler was looking for including information about "roots" and save him from loading a page of no use to him.
Always include title and description tags
Even if Google does not always use the meta tag description that you write for your webpage, it is still important to include it. Otherwise, you might find in Google search results just the top words Google encounters in your webpage, such as "home, contact us", and these will never persuade anyone to open your page.
One thing to note is that Google does not use your description meta tag to decide whether to show your link. However, it will use your title meta tag to rank your listing, making this tag especially important to include.
In the old days, people spent a lot of effort adding keyword tags. Since Google hasn't used these tags for a long time, adding these tags are now hardly worth the effort, although you might find a few minor search engines that take them into account.