A DSO stands for Deep Space Oject. A DSO can come in many forms, such as Galaxies, Nebulea and Star clusters. Some targets such as M31 (The Andromeda galaxy) and M42 ( The Orion nebula) can be seen with the naked eye.
Most DSOs are outside the capabilities of the Human eye. So you will need a pair of binoculars or telescope. Beyond this, many fainter targets will only be found by imaging.
For a great selection of binoculars and telescopes, visit the Northern Optics website HERE