Canon

Acronym Almost sensible wording Explanation
AF Auto Focus Provides auto-focus
AFD Arc Form Drive Old design, slower auto-focusing
AL Aspheric Lens Used to minimize aberrations
CA Circular Aperture lenses Aperture blades to give as circular an iris shape as possible (not the standard Chromatic Aberration)
CA Chromatic Aberrations Purple fringes with high contrast pixels
CaF2 Fluorite element Rare earth minerals to improve the optical qualities
DO Diffractive Optics Special lens design that is supposed to rival the L lenses
EF EF Mount The new Canon mount introduced in 1987
EF-S EF-S Mount Lens designed for APS-C sensors only
EMD Electro-Magnetic Diaphragm All Canon EOS lenses use an electrically controlled aperture
Float Floating elements To improve the close focusing
FP Focus Preset A single focus distance can be preset and instantly returned to
FS Focus Range Selector You can restrict the focus range for faster operation
I/R Internal focusing Improves the speed of the auto-focusing
IS Image Stabilizer Minimizes blur caused by camera shake
L L Series Lens Canon professional level lens
MM Micro Motor focusing motor Old design, slower focusing than USM
SF Soft Focus Defocusing of image, creates a blur in the 135/2.8 SF
Super UD Super ultra low dispersion glass Extremely rare earth minerals to improve the optical qualities
TS-E Tilt Shift Lens Lens capable of tilt and shift movements
UD Ultra-low dispersion glass Rare earth minerals to improve the optical qualities
USM Ultrasonic Motor High-speed auto-focusing

Nikon

Acronym Almost sensible wording Explanation
AF Auto Focus Provides auto-focus
ASF Aspherical Lens Elements Improves the optical quality of the lens
CRC Close-Range Correction Improves the optical quality of fisheye, wide angles, and macro / micro lenses
D Distance Information The D-type and G-type Nikkors lenses send the subject-to-camera distance information to the camera. Use in EXIF and for the matrix metering and the fill-in flash
DC AF DC Defocusing of image, creates a blur in portrait lenses
DX DX Nikkor Lens for the APS-C Nikon sensor only
ED Extra-low Dispersion Glass Rare earth minerals to improve the optical qualities
FX FX Nikkor Lens for both the full frame and the APS-C Nikon sensor
IF Internal Focusing The lens can focus without changing its size
M/A Manual/Auto Mode Allows to operate in manual focus while in auto-focus
N Nano Crystal Coating Nikon’s premium multi-layer lens coating
PC Perspective Control Lens capable of tilt and shift movements
RF Rear Focusing Improves the speed of the auto-focusing
SIC Super Integrated Coating Nikon’s standard multi-layer lens coating
SWM Silent Wave Motor High-speed auto-focusing
VR Vibration Reduction Minimizes blur caused by camera shake