What is stock pilling?

how mine wepons is concetred stock pilling?

Well there's no set in stone definition of stockpiling. By that I mean, stockpiling isn't defined by like "50 or more weapons" or something like that. So really it's up to you to make the decision if you can consider someone stockpiling weapons or not. Basically, "A stockpile is a pile or storage location for bulk materials." (wiki), so it's up to you really.