Drilling is a general term for the boring of a round hole into a work piece. In practice there are a wide variety of different drilling operations.
Most drilling involves the use of a twist drill to produce holes ranging from 0.1mm up to 50.0mm in diameter. Possible depths vary depending on the drill diameter but as a general rule, the smaller the hole, the shallower the depth that is possible.
Other variations on basic drilling may include flat bottoming of drilled holes, counter-boring and countersinking.
Reaming is usually carried out after drilling and is used to accurately size a hole and apply a smoother finish that what can be achieved from drilling alone. Reaming can be carried out by hand or by machine.
Reamers can be of the fixed size, machine type reamers, or the hand operated, adjustable type. Fixed size reamers can be selected to accurately give a variety of different fits (e.g. H7 reamer for dowels) or tapered reamers for nozzle openings and tapered pins.
Similar depth restrictions apply to reamers as to drilling. Some examples of where reaming is used is to size holes for dowels, ejector pins and to size bushes for shaft running fits.