straight tip (ST)
Designation for the "straight tip" connector developed by AT&T. This optical connector features a physically contacting non-rotating 2.5mm ferrule design and bayonet connector-to-adapter mating. The bayonet housing may be metallic, ceramic, or plastic. Some people call it "stick and twist" because that's the motion used in attaching it to a device.
subscriber connector (SC)
Designation for an optical connector featuring a 2.5mm physically contacting ferrule with a push-pull mating design. This connector is recommended in the TIA/EIA-568-A Standard for structured cabling. This type of optical fiber connector is identified by the square cross-section of its plastic housing. Some people call this "snap and click" or "stick and click" because you press it into a device until you hear the click.
fiber connector (FC)
A round, threaded optical fiber connector that was developed by Nippon Telephone and Telegraph in Japan. The FC connector is good for single-mode or multimode fiber and applications requiring low back reflection. The FC is a screw-on type connector and is prone to vibration loosening.
Lucent connector (LC)
A small form factor SC-style connector with RJ45-type locking mechanism developed by Lucent. Check out http://www.lcalliance.com for more details.
MT-RJ (RJ is "registered jack"; not sure what the MT is, I think it has something to do with the ferrules)
A small form factor fiber connector that features a high-density design and RJ45-type locking mechanism. From AMP / Siecor (now Corning Cable Systems). Check out http://www.mtrj.com for more details.
Hope this helps.
