Speed dial is a phone feature that stores a number under a single button or a single digit, so you can call someone without typing the whole number. You press and hold 1, and it rings your mother. It comes from the age of landlines and early mobile phones, when numbers had to be typed by hand every time — so the feature saved real trouble. Today's smartphones make it nearly pointless (you tap a face, or say a name), and younger people may only half-know the term. It works as a noun — 'put me on speed dial', 'she's number 3 on my speed dial' — and as a verb, usually hyphenated: 'he speed-dialled his lawyer'. British spelling doubles the l (speed-dialled), American does not (speed-dialed). The phrase has outlived the technology as an idiom. 'You're on my speed dial' now means 'you are one of the few people I call all the time, you matter'. And 'he has the White House on speed dial' means he has powerful friends he can reach instantly — nobody imagines an actual button. That figurative use is where you are most likely to meet it now. Note also that 'dial' itself is a fossil: it means the round face of an old telephone that you turned with your finger. We still 'dial' numbers on phones that have no dial at all.