An action mapping that uses wildcards in the action name attribute to configure actions in the Struts 2 framework. Wildcards can be used to combine similar mappings into one more generic mapping.
Wildcards, and their possible applications in Struts2 action mapping are both diverse and powerful.
Rather than attempt to explain it all here, just go read the article here: https://cwiki.apache.org/WW/wildcard-mappings.html