globs, more properly called [shell] patterns, and also known as wildcard expressions, are instances of a pattern-matching language used in many, esp. POSIX-like shells, to match filenames and strings: e.g., *.c is a glob for C source files and matches any file whose suffix (extension) is .c
Glob patterns are distantly related to regular expressions, but have simpler, incompatible syntax and offer fewer features.
Their typical use is to match multiple filenames or paths based on an abstract pattern; e.g.:
*.cpplog-user*-[0-9][0-9].gz
A major difference between globs and regular expressions (tag: regex) is there are far fewer meta-characters for globbing, and there are no duplication symbols (quantifiers). Most notably, * and ? by themselves match any (possibly empty) sequence of characters and any single character, respectively.
Wikipedia has a page on glob patterns.
On Unix systems, the POSIX pattern notation defines the notation for POSIX-compatible shells.
Generally, it is the shell itself that processes a glob pattern specified as an unquoted argument to a command: it expands it to all matching filenames and passes them as individual arguments to the command given, a process known as filename or pathname expansion.
Note that use of patterns in POSIX-like shells is not restricted to filename expansion: they are also used in parameter expansions (e.g., ${HOME##*/} to strip the directory path from a path) and string-matching operations (such as with case ... esac).
