Mounted Optics are capable of being mounted and sighted in. They come in many shapes and sizes. The more compact thermal sights and digital night vision scopes can be used as monoculars as well. You can remove them and put them back on and the scope will still hold zero.

These rifle scopes come in 2 forms as well:

Mounted Optics With Night Vision

Mounted optics with night vision are thermal sights that can be mounted to a weapon that uses night vision. These sights are generally usable in the daytime, but also have the ability to be used in total darkness with the help of an infrared light.  They generally attach to a weapon using a picatinny rail mount, giving the user a wide range of usability on most types of weapons.

Mounted Optics With Thermal Imaging

Mounted optics with thermal imaging are optics that can be mounted to a weapon that use thermal imaging. These thermal sights are usable in the daytime, but really shine when  used in total darkness because the unit picks up heat signatures. These digital night vision scopes generally attach to a weapon using a picatinny rail mount, giving the user a wide range of usability on most types of weapons.