This is a BLACKHAWK Inside Waistband Holster known as the Inside Pant, model 73IP05BK-L.
Blackhawk's popular inside-the-pants design is soft to the touch and easy to draw thanks to its laminate suede-like outer shell and smooth nylon lining.
Features:
No retention strap
Belt clip slips over pants or belt to retain holster
Size 5
Left hand
Fits Glock 26/27/33 and other sub-compact 9/.40