What does the '-5p' or '-3p' suffix in a miRNA name mean?

When a microRNA precursor (pre-miRNA) stem-loop is processed by DICER, it produces two potential mature strands: one from the 5' arm and one from the 3' arm of the stem-loop. The suffixes '-5p' and '-3p' indicate which arm of the precursor the mature miRNA strand comes from. For example, miR-21-5p comes from the 5' arm of the miR-21 stem-loop. Both strands can have distinct biological targets and activity levels — they are not identical molecules. The Yenos panel specifically measures the -5p forms of miR-21 and miR-375, and the -3p form of miR-141, because these are the predominant strands documented in cancer research for each marker.