Wikipedia says

UNIX interprets a space as a separator not as a character.
*
A wild card character that matches any group of characters of any length, allowing a user to specify a large group of items with a short string. For example, to specify all the files that start with 'abc', you use abc*.
?
A wild card character that matches any single character. Thus ls ??? lists files in the current directory whose names are only three characters long, while ls ???.* lists those files with a three letter main name and any extension.
[..]
A set of characters that can be matched. Thus ls [a-c]*.??? lists all files that begin with a, b, or c and have a three letter extension and lpr [ad]* prints all files that begin with a or d.
$
Indicates that the following text is the name of a shell (environment) variable whose value is to be used.
|
Separates commands to form a pipe (see redirection in "Intermediate Use Of The UNIX Operating System").
<
Redirect the standard input (see redirection in "Intermediate Use Of The UNIX Operating System").
>
Redirect the standard output (see redirection in "Intermediate Use Of The UNIX Operating System") to replace current contents.
>>
Redirect the standard output (see redirection in "Intermediate Use Of The UNIX Operating System") to append to current contents.
>&
Redirect the standard output and standard error (see redirection in "Intermediate Use Of The UNIX Operating System") to replace current contents.
>>&
Redirect the standard output an standard error (see redirection in "Intermediate Use Of The UNIX Operating System") to append to current contents.
%
Introduces a job name (see multitasking in "Intermediate Use Of The UNIX Operating System").
&
Place a process into the background (see multitasking in "Intermediate Use Of The UNIX Operating System").
()
Encloses a sequence of commands or pipes to be executed as a single command.
!
Precedes a history substitution (see "man history")
;
Separates sequences of commands (or pipes) that are on one line.
&&
Separates two sequences of commands or pipes the second of which is executed only if the first succeeds.
||
Separates two sequences of commands or pipes the second of which is executed only if the first fails.
\
Used to "quote" the following metacharacter so it is treated as a plain character, as in \*.