In a connected feature the points are joined by lines. Example of connected features are contours, streams, roads etc.
Unconnected features appear in the Plan Window as a set of isolated points. It is often useful to group points together into unconnected features. Displaying points in a single unconnected feature is generally faster than displaying the points as individual features.
An example of an unconnected feature is a regular grid (rows and columns of xyz points) which has been imported into the terrain module. It will display much faster when stored as a single feature.
Connected features can be selected by clicking on any line segment. Whereas unconnected features can only be selected by clicking on one of the points.