A heap overflow occurs when a program writes more data to a block of memory allocated on the heap than it can hold. This can lead to overwriting adjacent memory, causing unpredictable behavior, crashes, or security vulnerabilities. The heap is a region of a computer's memory used for dynamic memory allocation, where variables are stored during runtime. Heap overflows can be exploited by attackers to execute arbitrary code or manipulate program behavior. Proper memory management techniques, such as bounds checking and using safe memory allocation functions, can help prevent these vulnerabilities. Understanding heap overflows is crucial for software developers and security professionals to ensure robust applications.