MemTest86 is a diagnostic tool designed to test the memory (RAM) of a computer for errors. It runs a series of tests to identify any issues that may cause system instability, crashes, or data corruption. By booting from a USB drive or CD, users can run the program outside of their operating system, ensuring a thorough examination of the memory. The software is widely used by technicians and enthusiasts to troubleshoot hardware problems. It supports various memory types and can detect a range of errors, helping users determine if faulty RAM is the source of their computer issues.