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ASCII /as'kee/ n.
[originally an acronym (American Standard Code for Information Interchange) but now merely conventional] The predominant character set encoding of present-day computers. The standard version uses 7 bits for each character, whereas most earlier codes (including early drafts of of ASCII prior to June 1961) used fewer. This change allowed the inclusion of lowercase letters -- a major [win] -- but it did not provide for accented letters or any other letterforms not used in English (such as the German sharp-S or the ae-ligature which is a letter in, for example, Norwegian). It could be worse, though. It could be much worse. See [EBCDIC] to understand how. A history of ASCII and its ancestors is at http://www.wps.com/texts/codes/index.html.
Computers are much pickier and less flexible about spelling than humans; thus, hackers need to be very precise when talking about characters, and have developed a considerable amount of verbal shorthand for them. Every character has one or more names -- some formal, some concise, some silly. Common jargon names for ASCII characters are collected here. See also individual entries for [bang], [excl], [open], [ques], [semi], [shriek], [splat], [twiddle], and [Yu-Shiang Whole Fish].
This list derives from revision 2.3 of the Usenet ASCII pronunciation guide. Single characters are listed in ASCII order; character pairs are sorted in by first member. For each character, common names are given in rough order of popularity, followed by names that are reported but rarely seen; official ANSI/CCITT names are surrounded by brokets: <>. Square brackets mark the particularly silly names introduced by [INTERCAL]. The abbreviations "l/r" and "o/c" stand for left/right and "open/close" respectively. Ordinary parentheticals provide some usage information.
! Common: [bang]; pling; excl; shriek; ball-bat; <exclamation mark>. Rare: factorial; exclam; smash; cuss; boing; yell; wow; hey; wham; eureka; [spark-spot]; soldier, control." Common: double quote; quote. Rare: literal mark; double-glitch; <quotation marks>; <dieresis>; dirk; [rabbit-ears]; double prime.# Common: number sign; pound; pound sign; hash; sharp; [crunch]; hex; [mesh]. Rare: grid; crosshatch; octothorpe; flash; <square>, pig-pen; tictactoe; scratchmark; thud; thump; [splat].$ Common: dollar; <dollar sign>. Rare: currency symbol; buck; cash; string (from BASIC); escape (when used as the echo of ASCII ESC); ding; cache; [big money].% Common: percent; <percent sign>; mod; grapes. Rare: [double-oh-seven].& Common: <ampersand>; amper; and, and sign. Rare: address (from C); reference (from C++); andpersand; bitand; background (from sh(1)); pretzel; amp. [INTERCAL called this `ampersand'; what could be sillier?]' Common: single quote; quote; <apostrophe>. Rare: prime; glitch; tick; irk; pop; [spark]; <closing single quotation mark>; <acute accent>.( ) Common: l/r paren; l/r parenthesis; left/right; open/close; paren/thesis; o/c paren; o/c parenthesis; l/r parenthesis; l/r banana. Rare: so/already; lparen/rparen; <opening/closing parenthesis>; o/c round bracket, l/r round bracket, [wax/wane]; parenthisey/unparenthisey; l/r ear.* Common: star; [[splat]]; <asterisk>. Rare: wildcard; gear; dingle; mult; spider; aster; times; twinkle; glob (see [glob]); [Nathan Hale].+ Common: <plus>; add. Rare: cross; [intersection]., Common: <comma>. Rare: <cedilla>; [tail].- Common: dash; <hyphen>; <minus>. Rare: [worm]; option; dak; bithorpe.. Common: dot; point; <period>; <decimal point>. Rare: radix point; full stop; [spot]./ Common: slash; stroke; <slant>; forward slash. Rare: diagonal; solidus; over; slak; virgule; [slat].: Common: <colon>. Rare: dots; [two-spot].; Common: <semicolon>; semi. Rare: weenie; [hybrid], pit-thwong.< > Common: <less/greater than>; bra/ket; l/r angle; l/r angle bracket; l/r broket. Rare: from/{into, towards}; read from/write to; suck/blow; comes-from/gozinta; in/out; crunch/zap (all from UNIX); tic/tac; [angle/right angle].= Common: <equals>; gets; takes. Rare: quadrathorpe; [half-mesh].? Common: query; <question mark>; [ques]. Rare: whatmark; [what]; wildchar; huh; hook; buttonhook; hunchback.@ Common: at sign; at; strudel. Rare: each; vortex; whorl; [whirlpool]; cyclone; snail; ape; cat; rose; cabbage; <commercial at>.V Rare: [book]. Common: l/r square bracket; l/r bracket; <opening/closing bracket>; bracket/unbracket. Rare: square/unsquare; [U turn/U turn back].\ Common: backslash, hack, whack; escape (from C/UNIX); reverse slash; slosh; backslant; backwhack. Rare: bash; <reverse slant>; reversed virgule; [backslat].^ Common: hat; control; uparrow; caret; <circumflex>. Rare: xor sign, chevron; [shark (or shark-fin)]; to the (`to the power of'); fang; pointer (in Pascal)._ Common: <underline>; underscore; underbar; under. Rare: score; backarrow; skid; [flatworm].` Common: backquote; left quote; left single quote; open quote; <grave accent>; grave. Rare: backprime; [backspark]; unapostrophe; birk; blugle; back tick; back glitch; push; <opening single quotation mark>; quasiquote.{ } Common: o/c brace; l/r brace; l/r squiggly; l/r squiggly bracket/brace; l/r curly bracket/brace; <opening/closing brace>. Rare: brace/unbrace; curly/uncurly; leftit/rytit; l/r squirrelly; [embrace/bracelet].| Common: bar; or; or-bar; v-bar; pipe; vertical bar. Rare: <vertical line>; gozinta; thru; pipesinta (last three from UNIX); [spike].~ Common: <tilde>; squiggle; [twiddle]; not. Rare: approx; wiggle; swung dash; enyay; [sqiggle (sic)].
The pronunciation of # as `pound' is common in the U.S. but a bad idea; [Commonwealth Hackish] has its own, rather more apposite use of `pound sign' (confusingly, on British keyboards the pound graphic happens to replace #; thus Britishers sometimes call # on a U.S.-ASCII keyboard `pound', compounding the American error). The U.S. usage derives from an old-fashioned commercial practice of using a # suffix to tag pound weights on bills of lading. The character is usually pronounced `hash' outside the U.S. There are more culture wars over the correct pronunciation of this character than any other, which has led to the [ha ha only serious] suggestion that it be pronounced `shibboleth' (see Judges 12:6 in an Old Testament or Tanakh).
The `uparrow' name for circumflex and `leftarrow' name for underline are historical relics from archaic ASCII (the 1963 version), which had these graphics in those character positions rather than the modern punctuation characters.