Wiktionary
n. A usually hand-held grinder which uses a pair of internal gears to place the rotational axis of the grinding or cutting wheel perpendicular to that of the driving motor.
Wikipedia
An angle grinder, also known as a side grinder or disc grinder, is a handheld power tool used for cutting, grinding and polishing.
Angle grinders can be powered by an electric motor, petrol engine or compressed air. The motor drives a geared head at a right-angle on which is mounted an abrasive disc or a thinner cut-off disc, either of which can be replaced when worn. Angle grinders typically have an adjustable guard and a side-handle for two-handed operation. Certain angle grinders, depending on their speed range, can be used as sanders, employing a sanding disc with a backing pad or disc. The backing system is typically made of hard plastic, phenolic resin, or medium-hard rubber depending on the amount of flexibility desired.