The focus motor moves the lens in order to autofocus. For system cameras, having a focus motor in the camera's body allows you to use a wide range of lenses, including lenses which do not have their own focus motor. For compact cameras, a focus motor is usually built-in.
We consider a lower weight better because lighter devices are more comfortable to carry. A lower weight is also an advantage for home appliances, as it makes transportation easier, and for many other types of products.
The more focus points the more flexibility in picking which part of the scene to focus on. They also give the image sensor a better probability in identifying the right area of the scene to focus on in more automatic modes.
The number of megapixels determines the resolution of the images captured with the main camera. A higher megapixel count means that the camera is capable of capturing more details. However, the megapixel count is not the only important element determining the quality of an image.
The device has a standard memory slot (such as an SD or micro SD card slot) that enables you to extend the built-in internal storage with affordable memory modules, or easily retrieve data, such as photographs, from the memory card.