Filter
Operators that need 1 or more inputs (to create a meaningful output) are called Filters in TouchDesigner, like a Math CHOP. "Inputs" are both the wires from other operators, and references to other operators in OP parameters.
Filters are the lighter shaded operators in the OP Create Dialog.
See their counterparts Generators.
Operators may have inputs defined by Parameters that are Path references to other operators, that are from any Operator Family.