When the FDA accepts a drug application it assigns a review track. Standard review targets a decision in ~10 months; priority review targets ~6 months, for drugs that, if approved, would be a significant improvement in safety or effectiveness.
Standard review~10 months
Priority review~6 months
Priority review is a six-month FDA review goal granted when a drug would, if approved, significantly improve the safety or effectiveness of treatment; standard review carries a roughly ten-month goal. The designation shortens the clock but does not lower the evidence bar for approval.
What it signals, and doesn't
Priority review reflects the potential importance of the drug, not a higher approval probability. Plenty of priority-review drugs get CRLs. It mainly compresses the timeline: useful for catalyst timing. Related: what is a PDUFA date.