The Aggregate Design Canvas is a tool meant to be used as a part of design-level domain modelling activities.
An aggregate is a lifecycle pattern originally described by Eric Evans. By aggregate, we understand a graph of objects that is a consistency boundary for our domain policies. Depending on the design of the aggregate we can either enforce them (make them invariant) or be forced to have corrective policies in place. Because of that, it is important to design the boundaries of aggregates well, as they impact behaviours modelled within our domain.
The canvas has a suggested order of working through it, that helps to iteratively discuss different aspects of the aggregate design.