a sheath (usually leather) for carrying a handgun
"He quickly drew his weapon from the leather holster on his belt to check if it was still loaded."
a belt with loops or slots for carrying small hand tools
"The cowboy checked his leather holster to ensure his pocket knife and compass were securely tucked in before heading out on the trail."
A case for carrying a tool, particularly a gun, safely and accessibly.
"The detective quickly drew his weapon from the leather holster strapped to his belt during the raid."
To put something in a holster.
"After checking that his weapon was safe, he carefully holstered it back into its leather case on his belt."