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. Google specifies no character limit and truncates the snippet according to the available display width; as a house editorial guideline we therefore work with 140 to 158 characters plus a concrete statement of benefit – our own convention, not a Google requirement. Independently of that, Google often generates the snippet itself from the page text when an extract fits the particular query better: the meta description is a suggestion, not an instruction.