Prioritizing the requirements in the product backlog is one of the most important responsibilities of the product owner. There are several ways to do it, one of the most popular technique is MoSCoW. It is a Product backlog refinement technique, where:
Mo stands for Must be
S stands for Should be
Co stand for Could be
W stands for Won’t be
Each requirement will have the priority which would be tagged to MoSCoW, with “M” being the highest and “W” being the lowest priority.