There are three outcomes for a reaction at an asymmetric atom. Consider the replacement of a group X by Y in the following reaction
If (A) is the compound obtained, the process is called retention of configuration.
If (B) is the only compound obtained, the process is called inversion of configuration.
If a 50 : 50 mixture of the above two is obtained then the process is called racemisation and the product is optically inactive, as one isomer will rotate light in the direction opposite to another.
In general if during a reaction no bond to the stereocentre is broken, the product will have the same general configuration of group around the stereocentre as that of reactant. Such a reaction is said to proceed with retention of configuration.