mAh - definition
An ampere-hour or amp-hour (Ah) is a unit of electric charge. Smaller batteries however, such as those in mobile phones and digital cameras, are often rated in milliampere-hours.
The milliampere-hour (mAh) is one-thousandth of an ampere-hour and is a technical term for how much electrical charge a particular battery will hold. As an example, using higher mAh batteries in a device with constant electrical consumption will theoretically give you longer operating times.