I'm not sure if you are in the United States or not, but "pre-stressing" has different connotations in different areas.
In the US, we separate pre-stressing from post-tensioning. In other parts of the world, the terms mean similar things. A further clarification is to add the term "pre-cast" to pre-stressing to differentiate it from post-tensioning.
Pre-cast, pre-stressing is usually a bonded tendon method using bare (uncoated) tendons. The tendons are "pre-stressed" based on design needs so as to cause a pre-compressed condition in tension members or in the tensile stress block of members. Therefore, when tension stresses are introduced to the member, there effects are reduced or negated. Pre-cast pre-stressing depends on the developed friction bond between the concrete and steel tendons to develop the stress distribution.
Post-tensioning may be with either bonded or unbonded tendons. For unbonded conditions, an anchor plate must be used in both sides of the member to provide anchorage for the tendons. The design effects are similar.