Meta Description
The meta description is an HTML element that summarises the content of a web page in one or two sentences and is often shown by Google as the descriptive text beneath the page title in search results.
In practice
It is not a direct ranking factor, but it affects click-through rate noticeably. Between 140 and 158 characters works well, together with a concrete statement of benefit and the most important keyword – otherwise Google frequently replaces the description with an extract of its own taken from the page.