The act of manually entering your web site URL into a search engine submission form in order to alert the search engine to the existence of your site.
Manual submission is no longer necessary. Most search engines require that at least one other web site links to yours before they will include your site in their index - and once another site links to yours the search engine will probably discover your web site before you can say "manual submission".
A mirror is a site that holds a copy of another site's files. Mirrors are usually set up in an attempt to spread server load over several servers where the site content is very popular. Many software download sites have mirrors set up in different countries to allow users to download from the mirror that will give them the fastest download.
A moderator (or mod) is a human who takes on the task of controlling the user-generated content on a web site. Online discussion forums often have moderators who can delete or move posts, ban users etc. This web site also makes use of a moderator who decides which new terms and edits are approved for publication in the dictionary.
Mosiac (properly NCSA Mosaic) was the first ever web browser, developed by the National Center for Supercomputing Applications (NCSA). The NCSA licensed the source code to several companies, notably to Netscape who developed the popular Netscape Navigator browser, later followed by Internet Explorer, Opera, Firefox, Safari and other browsers.
MP3 defines a standard for storing, compressing and transmitting digitial sound files. Developed in 1988 by Leonardo Chiariglione in Germany, MP3's claim to fame was its compression ratio. MP3 compresses sound files at a ratio of 12:1, making it ideal for later use on the Web.
Multimedia presentation are presentations that include more than one media type, for example text + images + video etc. Most web sites today can be considered multimedia sites as very few use only one media type.