Exclamation Mark. In programming used as an operator to test for non matching values. Logical NOT. E.g. a != b would mean a does not equal b.
Pound or Hash. Indicates or means the following text is a number. Also used to comment out lines of code in a CGI script.
Dollar sign. Commonly used in programming languages to indicate or declare variables.
Percentage Sign. Used in some programming languages to indicate or declare hashes or as a modulus operator in mathematic functions.
Left and right parnethesis. Used in most programming languages to either group and set precedence of multiplication operations or to group conditions as disparate conditions when performing conditional tests in if / else blocks of code.
Asterisk. Used in programming languages as a regular expression patter to search an unlimited number of characters with in a string. Also used as a multiplication operator.
Dash or Hyphen or Negative operator. Commonly used in domain names, either because it makes a web address easier to read, or as an alternative domain name because the domain name minus the dash was not available.
Forward slash. Directory separator on Unix machines and web servers. Windows File systems use the backslash as a directory separator, however the Windows IIS webserver can usually use either the forward or backslash.
Also the division operator in mathematic functions.
Question mark. Also used in URLs to indicate what follows is the Query String portion of the URL.
Pronounced : At. Character used in e-mail addresses to separate the username name and domain name. username @ domainname.com. Also used in some programming languages as a symbol for Arrays.
Ampersand. Used in programming languages to concantenate strings, indicate functions, or as a logical AND operator. Also used in HTML to print Special ASCII Symbols
Pipe. Used in programming languages as a Bitwse OR or if doubled up as Logical OR test operator.
Backslash. Used as a directory separator on Windows and DOS File systems.
Carret. Used in programming languages as a regular expression pattern to search string either from the start or to ignore the following characters.
Left and Right braces. Commonly used as syntax characters in programming languages.