Answer:A. When instructions are not allowed to move through the pipeline for one or more clock cycles due to a data or structural hazard.
Explanation:Pipeline stall is a term used to computer programming and software development,it also helps to protect the information in the pipeline from being overwritten by the following Pipeline stalling has helped programmers/ software developers to ensure effective and safe execution of projects. For microprocessors,the lack of pipeline stalls often increases the pipeline length.