Abbreviation: ZL = "Zoom Lock" (Tamron)

The abbreviation ZL means "Zoom Lock" and is seen on Tamron products.

Explanation from Tamron

Another original Tamron mechanical engineering concept is the Zoom Lock (ZL), a simple convenience feature that prevents undesired extension of the lens barrel when carrying the camera/lens unit on a neck strap.

See examples of effected products

See links