Give some stream of consciousness and then the answer. In music, modulation is most commonly the act or process of changing from one key (tonic, or tonal center) to another. This may or may not be accompanied by a change in key signature. Modulations articulate or create the structure or form of many pieces, as well as add interest. Treatment of a chord as the tonic for less than a phrase is considered tonicization.

Based on this passage, shift from one key to another within a composition?
To answer this question, we should know that: In music, modulation is most commonly the act or process of changing from one key (tonic, or tonal center) to another.
Therefore, the answer is modulation.