Glossary of Terms
OIS - Optical Image Stabilisation. A software controlled electro-mechanical system that counteracts unwanted movement of a camera when pressing the shutter button which can cause the resultant image to be blurred. It is usually built into the lens itself. There can be many reasons for unwanted movement including the act of pressing the shutter itself, external factors such as wind or vibration from sources like motors, engines or fans and internal sources such as the shutter itself or movement of associated mechanisms such as a moving mirror if the camera has one. What this means in practical terms is that images taken with slower shutter speeds than usual remain in focus. It is particularly beneficial when using long focal length lenses in poor lighting conditions such as indoor sports or street images under artificial light, but there many potential applications. The effectiveness of such systems is measured using a scale of stops, so a one stop improvement would mean that you can double your exposure time and still retain sharpness across the image. Most systems claim a two to four stop improvement which means theoretically you can make sharp images which have exposure times between four and 16 times longer than would normally be possible.
IBIS - In Body Image Stabilisation. A system similar to OIS, but it is always mounted within the camera body. These are claimed to be more effective than lens mounted systems as they control camera movement around more planes of movement. They can also be combined with OIS systems which are compatible and some systems claim up to seven stops of compensation meaning you can effectively handhold images in the dark, or even do long (several seconds or more) exposure shots without using a tripod. However the key word there is 'claim' as results are often subject to more variables than camera movement, subject movement being one.