Scaling is the removal of hard deposits that build up on tooth enamel and just under the gumline. These deposits, often referred to as tarter, are more properly referred to as calculus. The accumulation of calculus is the first step in causing gingivitis which eventually will lead to periodontitis and loss of bone.
In your general dentist's office scaling is performed as part of your regular cleaning to prevent or treat gingivitis. In a periodontal office it is performed in conjunction with root planing to treat periodontitis and bone loss