Digital Tutors: Nuke Gizmo
A gizmo in nuke means a series of nodes that produces a specific output. In the example here, the nodes on the left clamps the image, selects the brightest points by raising the blackpoint, does a blur, then multiply it by half. They do the same thing as a single glow node. Thus a gizmo is like a mother node in a sense.
We can make gizmos grouping them and start adding attributes which connects to important values using parent/child expressions.
This could make your compositing life much easier! There are gizmos around the internet available for download, it is up to you to try them out.