Lead Time is the time it takes from identifying a need (could be a customer problem, feature request, defect raised, technical enhancement etc.) to making a solution available to customers.
Having a shorter the lead time equates to more responsiveness.
To reduce the lead time in Scrum: a) a shorter sprint duration is recommended, b) work (PBIs) is divided in smaller slices, c) an emergent product backlog is used, d) a Work-In-Progress (WIP) limit is used during Sprint execution
A Self-Managing and Cross-Functional Scrum Team further improves the ability to improve the rate of value delivery hence a shorter Lead Time.