What is DAG node

A really basic word in rigging and it is usefull to know what is it originally. In Maya, a directed acyclic graph (DAG), defines elements such as the position, orientation, and scale of geometry. The DAG is composed of two types of DAG nodes, transforms and shapes. Transform nodes-Maintain transformation information (position, rotation, scale, etc.) as well as parenting information. For example, if you model a hand, you would like to apply a single transformation to rotate the palm and fingers, rather than rotating each individually-in this case the palm and fingers would share a common parent transformation node. Shape nodes-Reference geometry and do not provide parenting or transformation information. In the simplest case, the DAG describes how an instance of an object is constructed from a piece of geometry. For example, when you create a sphere, you create both a shape node (the sphere) and a transformation node that allows you to specify the sphere's position, scale, or rotation. The transformation node's shape node is its child.