Final answer:
Stack timelines, also known as layered or parallel timelines, are tools used in social studies to compare different events or periods that occurred simultaneously but in different places, or different aspects of a single event, enhancing understanding of historical relations and contexts.
Step-by-step explanation:
In social studies, specifically in historical contexts, stack timelines, also known as layered timelines or parallel timelines, are visual representations used to compare different events or periods that occurred at the same time but in different places, or different aspects of a single event or period. These stack timelines help to see historical events in relation to each other, providing a fuller understanding of the global picture at any given point in history. For instance, a stack timeline might show the developments in Europe, Asia, and the Americas during the 18th century side by side. This can help students understand how events in different parts of the world influenced each other or occurred independently.