I.S. (Image Stabilisation) in a camera or lens can permit the use of shutter speed 2 to 5 stops SLOWER, but still result in SHARP PICTURES.
When I was starting in photography many years ago, I was told...
“The rule of thumb to determine the slowest shutter speed possible for hand-holding without noticeable blur due to camera shake is to take the reciprocal of the 35 mm equivalent focal length of the lens, also known as the "1/mm rule". For example, at a focal length of 125 mm on a 35 mm camera, vibration or camera shake could affect sharpness if the shutter speed was slower than 1/125 second.” - Wikipedia
What happen if there is only enough light to allow F4 (max aperture) and 1/60 for the ISO 400 film you are using? No, you have no tripod and monopod either, what then?
Fast forward to present...
You have IMAGE STABILISATION!
To understand the concept and the working of IS, I suggest you read this excellent write up.
The mechanism of an image stabilisation can be found in either the lens or built into the camera.