Computer programs have specific memory allocated to them known as a buffer that allows for the temporarily store data. When the program exceeds the boundaries of the buffer, it starts to write data to adjacent memory. When this occurs, it is called buffer overflow. Essentially, the program's memory buffer has exceeded its limit.
Buffer overflows can cause incorrect program behavior and issues, or even result in memory access issues. On computers running Windows versions older than Vista, these errors may cause a blue screen error.