A pipeline stall, also known as a pipeline bubble, is a delay in the instruction processing pipeline of a computer processor. It occurs when the next instruction cannot proceed to the next stage because the previous instruction has not completed, often due to data dependencies, resource conflicts, or cache misses. In cybersecurity, pipeline stalls can be exploited in side-channel attacks, where attackers measure timing differences to infer sensitive information. Understanding pipeline stalls is important for both optimizing system performance and mitigating certain security vulnerabilities in modern processors.