Lead time is the wait between deciding to do something and being able to do it. In a trade business it has two meanings, and a quote needs both. The first is supplier lead time: how long made-to-order or special-order items take to arrive after you order them, such as toughened glass, a garage door built to an opening, a switchboard part, steel back from the galvaniser or joinery from the workshop. The second is your own booking lead time: how far ahead your diary is full, and so how soon after a yes the work can begin.
A customer hears "you can start once I accept" unless the quote says otherwise. Telling them the real wait, and what it depends on, stops the phone call on day four asking where you are.
In practice
A glazier quotes a frameless shower screen. The toughened panels take ten working days to arrive once ordered, the glazier orders only when the deposit has cleared, and the install diary is booked a week ahead. So the note reads: install about three weeks after the deposit clears, with the date confirmed when the glass is ready. A customer who accepts on a Friday and pays on the Monday knows not to expect anyone that week, and the glazier is not apologising for a delay that was always going to happen.
Lead times also connect to quote validity. Suppliers of made-to-order items often hold their own price for a limited time, and you place the order only after the customer says yes. Set the validity on your quote so that an acceptance on its last day still lets you order at the price you were given, or the margin on the job shrinks before it starts.
When a lead time is outside your control, say whose it is. "Glass is made to order by the supplier, currently ten working days" is a fact the customer can accept. "About two weeks" with no reason is a promise they will hold you to.