Procedural means the automatic generation of outputs based on live inputs and the current state of TouchDesigner. Dependency is the procedural mechanism in TouchDesigner, where if one piece of data changes, it automatically causes other operators and expressions to re-Cook. This assures all data is consistent in a TouchDesigner process, and causes all the output displays, UIs, devices and protocols to update in realtime.
If there is a change in an operator's output data or parameter value, it causes other operators downstream from it to cook. Downstream means operators that are connected to the output of a changed node, and operators (or their parameters) that refer to the changed operator (often visible as the dashed-lines in a network).
Python Data Dependencyedit
Because Python does not inherently have a procedural mechanism, Dependency Objects in TouchDesigner allow python data to cause downstream cooking when that data is changed.