Anson fastening fore-end is a British term for a spring-loaded bolt style stock attachment device used on some double-barrel shotguns.

There is an exposed push button at the forward tip of the fore-end that when pushed releases the stock piece.

A picture of one can be seen here ⇒.

Footnotes / Sources:

“Glossary ⇒.” Sporting Arms and Ammunition Manufacturers’ Institute. Ed. SAAMI’s Technical Committee. Web. 15-18 Jan. 2011.