What is OIS optical image stabilisation?
A camera technology that moves the lens itself to cancel out hand shake while you shoot.
OIS, or optical image stabilisation, is a mechanical system inside a phone camera. When your hand shakes, the lens moves in the opposite direction to keep the image steady on the sensor. This is different from electronic stabilisation (EIS), which fixes shake with software after or during capture. The result is a sharper photo without needing a tripod.
In daily use, the difference shows most in low light. OIS lets the camera keep the shutter open longer without blurring the shot, so night photos and indoor pictures look clearer. It also helps when recording video while walking or moving, and reduces shake in close-up shots. It does not make your hands perfectly steady, but it gives you a better chance of a usable photo.
When buying, look for OIS mentioned clearly in the rear camera specs, because some phones only offer EIS. OIS is common on the main lens, sometimes on a telephoto lens, but rarely on ultra-wide lenses. You do not need to understand the technical details; just check for OIS if you often shoot in dim light or record video.