What are the common phrases, words, abbreviations that are used on Stack Overflow, Server Fault, Super User, and Meta Stack Overflow?

This is meant to be a very quick overview, not an in-depth tutorial. When considering whether a term ought to be included, please use this test:

New user comes in and posts on day 1. What terminology or jargon are they likely to run into (comments, support, system messages, etc) that cannot be understood from the context without prior experience with the site (i.e. clear only if known). For example: "This is a dupe. Flag a diamond mod to close or migrate to SU." Huh? Can these instruction be made clear from the glossary? Is it clear for those for whom English is a second language.

Please:

• Edit the existing answer
• Insert relevant links to more detailed information on the term/phrase/abbreviation
• Add only factual information
• Keep it very, very brief, terse, and to the point
• Delete your own comments once they become irrelevant (integrated into the glossary)
• Use the Edit Summary box to note reasons for your edit, not comments

Please avoid:

• Opinion
• Using abbreviations, terms, and phrases inside a description
• Unverified information
• Uncommon terms, abbreviations, phrases
• Long descriptions
• Unnecessary detail - link to the relevant FAQ instead
• Citations or examples of usage
• Inside jokes that are not common on all of the trilogy (see meme thread for those)
• Common Internet jargon (i.e., IMHO, TL;DR, RTFM, etc.) unless usage here differs significantly