A meta description is a page summary specified in the HTML <meta name="description"> tag. It serves as the source for the snippet displayed below the title in search engine results pages (SERPs), helping users decide whether to click on a result. While not a direct ranking factor, it significantly affects click-through rates (CTR), making it an important element in SEO strategy.

Google states that there is no limit on how long a meta description can be and that the snippet is truncated as needed to fit the width of the device. In other words, there is no official threshold below which the whole text is guaranteed to appear, and the same text is cut at different points on desktop and on mobile; the figures shared in practice, about 155-160 characters for English and around 120 for Japanese, are rules of thumb based on observation rather than guaranteed limits. Because truncation happens at the end, placing the essential information first and using the rest for supplementary detail is safer than aiming for an exact character count.

Writing effective meta descriptions involves several key points. First, accurately summarize the page content and address the user's search intent. Wording that states concretely what the reader will learn ("with formulas and worked examples" rather than "explained in detail") lets the result stand out from the other pages listed for the same query. When search terms appear within the meta description, they may be shown in bold in the snippet, so including the words of the intended query as they are can help visibility.

When no meta description is set, Google automatically extracts relevant portions from the page content based on the search query to generate a snippet. While these auto-generated snippets can sometimes be appropriate, writing a unique meta description for each page gives you control over the displayed summary. Reusing the same meta description across multiple pages should be avoided.

A common misconception is that a set meta description will always be displayed as-is. In reality, Google may ignore the meta description and generate its own snippet from the page content, especially when the meta description has low relevance to the search query. Also, meta descriptions and Open Graph's og:description serve different purposes; og:description is used when content is shared on social media.

For character counting, meta descriptions are one of the HTML elements where character count management matters most. Too short and they lack information to attract clicks; too long and they get truncated, losing their intended message. For English sites, a practical approach is to treat 120-160 characters as a working guideline and to check the text with a character counting tool.