markup : Formatting and other types of HTML code, such as Font tags to define the font style.

Meta robots tag : An HTML command in the head section (top part) of a Web page’s HTML code that gives instructions to search engine spiders whether to index the page and whether to follow its links.

metadata : Text that is added to the HTML of a page to describe it for a search engine.

meta-refresh : The automatic reloading of a Web page.

metasearch engine : A search engine that does not maintain a database of its own, but instead combines results from multiple search engines.

metric : A quantitative measure of something, such as a process, rate, or amount.

mirror : A full copy of a Web page or site.

multi-page analyzer : A program that measures the keyword density of multiple Web pages.

multivariate testing : Testing small changes to a Web site, such as the change of a certain font, or a button instead of an arrow. Typically, this involves testing many small changes to the same page at once instead of two totally separate pages, as in A/B testing.