Replication crisis is a problem where scientists have trouble repeating the results of another scientist’s study. This means that if one scientist does an experiment and finds a certain result, another scientist may not get the same result when they try the same experiment. It's often caused by things like mistakes in data, bias, or not doing enough experiments to be sure the results are right. It can make it harder for scientists to trust each other's work, which means it's harder to make progress and figure out new things.