Everybody can see your meta description in search result pages. That is a summary of what the page is about.

For instance, if you typed a search query for cheap flights to Hawaii and one search result showed the flight prices (i.e. in the meta description or title appearing as a search snippet), as shown in the example below, you would likely click on that link as opposed to other links above or below it.

"blog.woorank.com"

Search Engines might use description as snippets for your pages.

Text displayed beneath the title of a corresponding web page on the search results pages of a search engine. A web page summary and/or parts of the page that match the search keywords will be displayed.
"Google SEO guide"

Accurately summarize page’s content

Note that, accurately summarize not entire content of the document. Avoid writing something that has no relation to the content of the page.

Unique for each page

That helps both Search Engine and Users, especially in searches where user may bring up multiple on your domain.

The problem is how we can handle when we have a blog with thousand pages? It probably isn’t feasible, in this case maybe we should generate description based on each page’s content automatically.

Characters Length

There is no limit to the character in meta description, but only 150 - 170 characters was allowed in search results.

Practice with Odoo

Very simple that you can select "Promote > Optimize SEO" and insert page's description