Rowhammer is a hardware vulnerability found in dynamic random-access memory (DRAM) that allows an attacker to manipulate data stored in memory cells. By repeatedly accessing (or "hammering") specific rows of memory, an attacker can induce bit flips in adjacent rows, potentially altering sensitive information. This exploit can be used to bypass security measures and gain unauthorized access to systems. It affects various devices, including computers and smartphones, and poses a significant risk to data integrity and system security, prompting ongoing research into mitigation techniques and hardware design improvements.