In a shell environment, the term wild cards refers to metacharacters that are then expanded (also referenced as globbed) into a series of file names.
See glob for a Tcl function which provides some wild card expansion.
One concept that is sometimes hard for people to grasp is that wild cards are often handled transparently to the user.
That is to say, on Unix, before a command ever sees a command line from a shell, the shell has expanded the wild cards into file names.
However, other shells, such as Tcl, do not do such wild card expansions automatically. The programmer of an application is responsible to either expand them (via glob) or to invoke an external command which then expands the wild cards.
Glob-style wild-card characters
* matches any string of characters (including the empty string)
? matches any single character.
[...] matches a set of characters (need more detail)
{alt1,alt2} matches alternatives (but not in [string match]) (Wiki bug: can't have unbalanced braces inside font context, so alt1 and alt2 are erroneously bold.)
\\ forces the next character to be interpreted as a literal. (Wiki bug: single backslash causes crash.)
ab{c,?c}d Matches any string 4 or 5 characters long with ''ab'' at the start and ''cd'' at the end.