In simple terms, globbing refers to pattern matching. Bash uses simple globbing like,
echo l* which expand to list of files in current directory that start with letter
l. Of course , as you can guess, it's simple and limited.
extglob. As you can guess, it stands for
extended globbing. This option allows for more advanced pattern matching. From
extglob If set, the extended pattern matching features described
above under Pathname Expansion are enabled.
And a little before that:
If the extglob shell option is enabled using the shopt builtin, several
extended pattern matching operators are recognized. In the following
description, a pattern-list is a list of one or more patterns separated
by a |. Composite patterns may be formed using one or more of the
Matches zero or one occurrence of the given patterns
Matches zero or more occurrences of the given patterns
Matches one or more occurrences of the given patterns
Matches one of the given patterns
Matches anything except one of the given patterns
There's multitude of ways in which
extglob can be used. Quite a few good examples are provided in Linux Journal and Greg's wiki.