______ is defined as the interface between peripheral equipment and digital systems.

The term that best describes the interface between peripheral equipment and digital systems is indeed "Input and output." In the context of digital systems, the input refers to the data or signals received from various peripherals, which can include sensors, switches, and other devices. Output, on the other hand, pertains to the processed information that the digital system sends back to peripheral devices like actuators, displays, or alarms.

Input and output are critical components of any digital system because they facilitate communication and interaction between the system and its surrounding environment. This interaction results in data collection for processing (input) and the execution of commands or the display of information (output). By effectively integrating input and output, a digital system can perform its intended functions and respond dynamically to various operational conditions.

The other options highlight relevant concepts within systems but do not specifically address the interface aspect. Control refers to the mechanisms and strategies used to regulate system performance. Process variables focus on the measurable elements within a system that reflect its state or operation. Meanwhile, process encompasses the overall series of actions or operations that the system undertakes. While these terms are significant in their own right, they do not succinctly capture the idea of interfacing between peripherals and digital systems as input and output do.