Lead time is the total time from when a piece of work is requested to when it is delivered, including any time it waits before work starts.
Lead time is what the customer experiences. A bug fixed in two hours still has a lead time of three weeks if it sat in the backlog for three weeks first.
Example
A feature is requested on 1 March, started on 20 March and shipped on 25 March. Its lead time is 24 days and its cycle time is 5 days.
Improving lead time
Keep the backlog short and ordered, and say no early to work that will never be done.