Final answer:
Gaps, or illegal addresses, are flagged in the MMU as illegal addresses, and any attempt to access them results in the process being aborted.
Step-by-step explanation:
Gaps, or illegal addresses, are flagged in the MMU as illegal addresses, and any attempt to access them results in the process being aborted. These gaps occur when there are unallocated memory locations between valid memory addresses. For example, if a program tries to access memory address 1000 when the valid addresses range from 500 to 800, it would be considered an illegal address or a gap. Accessing these illegal addresses can lead to program crashes or system failures.