Last updated October 13, 2012.

The following general-purpose tags are not specific to any particular project issue:

Accessibility
Affects the ability of people with disabilities or special needs (such as blindness or color-blindness) to use Drupal.
Across the finish line
This tag identifies issues that have been pushed some or most of the way there by a contributor who no longer has the ability to drive it. This allows core contributors to tackle them who want to help get cool improvements in, but who don't yet have the expertise (or time) to work on issues from scratch, and who want to build up their expertise. Note that this is different from the "Novice" tag, as these kinds of issues may require more Drupal experience or time than what we typically use the Novice tag for.
CSS
Involves the content or handling of Cascading Style Sheets.
Docs infrastructure
Infrastructure/code improvements related to documentation. Note that the Core Documentation team uses this tag, not the next one.
Documentation
Primarily changes documentation, not code. For Drupal core issues, select the Documentation component instead of using this tag. In general, component selection is preferred over tag selection.
Drupal.org upgrade
Involves a recent or proposed upgrade to the drupal.org website.
DrupalWTF
Worse Than Failure. Approximates the unpleasant remark made by drupal developers when they first encounter a particular (mis)feature.
DX
Enhances developer experience.
Favorite-of-Dries
Please do not use this tag unless your name is Dries Buytaert.
HTML5
Implements and supports the use of HTML5.
i18n
(Internationalization) Involves or affects multilingual / multinational support. Preferred over Translation.
Infrastructure
Issues relating to drupal.org infrastructure that are posted in other queues such as Project or Project issue tracking.
Javascript
Affects the content, performance, or handling of Javascript.
jQuery
Affects the version, handling, or usage of the jQuery javascript library.
Novice
Would make a good project for someone who is new to the Drupal contribution process. Preferred over Newbie.
PHP 5.3
Particularly affects sites running on PHP version 5.3.0 or later.
PostgreSQL
Particularly affects sites running on the PostgreSQL database.
Quick fix
Very small and simple change. Preferred over Quickfix.
Usability
Makes Drupal easer to use. Preferred over UX, D7UX, etc.
Views
Involves, uses, or integrates with views.
WYSIWYG
Involves an in-browser What-You-See-Is-What-You-Get content editor.