Non-Homogenous Aggregate

From Fmepedia

An Aggregate is a group of features - a set of individual graphic elements that the user has chosen to bring together (but not merge) as a single entity.

A Non-Homogeneous Aggregate (aka a Heterogeneous Aggregate) is where the features in the aggregate are not all of the same geometry type - for example a line, a polygon and a point feature. This is important because some formats only support the homogeneous type of aggregate.