Final answer:
The term used to describe the capability of a PC operating system to support the execution of multiple applications simultaneously on a single-processor system is Multitasking.
Step-by-step explanation:
The capability to support the simultaneous execution of multiple applications on single-processor systems is termed Multitasking. This feature allows a single CPU to manage different processes by quickly switching among them, which gives the illusion that these processes are happening at the same time. Although they are actually being processed very rapidly one after the other, the user perceives them as simultaneous because the switching is faster than human noticing. Multitasking is essential for the efficient operation of a system, as it enhances system utilization and responsiveness. It's important to note that while multithreading involves multiple threads within the same application, multiprogramming refers to loading several programs at once, and multiprocessing refers to the use of two or more CPUs within a single computer system.