The Daily Scrum is a 15 minute event held at the same time and place every working day of the Sprint. The Developers use it to inspect progress towards the Sprint Goal and to adapt the Sprint Backlog, and what comes out of it is an actionable plan for the next day of work.
The phrase actionable plan carries the whole event. A Daily Scrum that ends without anybody knowing what they will do differently has spent 15 minutes and produced nothing.
What the 15 minute timebox protects
Fifteen minutes is short enough that the event cannot become the work. The Daily Scrum surfaces problems, and solving one properly usually takes longer than the meeting has time for, so the discipline is to name the problem, agree who will carry it and take the conversation outside. An event generous enough to solve everything it uncovers stops being a replan and becomes a working session that most of the team sits through without needing to be there.
The fixed time and place work the same way. Deciding when and where to meet is a small cost paid every day, and removing it leaves the Developers with one less thing to arrange.
Who the Daily Scrum is for and who runs it
The Daily Scrum is for the Developers, and it is theirs to run. They own the Sprint Backlog, so they are the only people who can adapt it, and the event exists to let them do that together rather than separately at their desks.
The Product Owner and the Scrum Master take part as Developers when they are actively working on Sprint Backlog items. Otherwise they hold no special position in the event. Others may attend, and none of them may turn the event into something delivered to them, because a group answering to an audience has started reporting and stopped replanning.
The Scrum Master ensures the event happens and stays inside its timebox, which is a service to the Developers and no claim on the event. The role of facilitator is optional here, and nothing in the Guide asks the Scrum Master to chair the Daily Scrum.
What the 2020 Guide stopped prescribing
The three questions many people still recite are no longer part of Scrum. What did I do yesterday, what will I do today and what is in my way appeared in the 2017 Guide as an example. Treating them as a rule produced a round of personal updates addressed to whoever seemed most senior in the room.
The Developers may select whatever structure and techniques they want, provided the event stays focused on progress towards the Sprint Goal and produces an actionable plan for the next day. Walking the board, talking through the Sprint Goal or something a team invented for itself all qualify. Nothing in Scrum requires the event to be held standing, requires every person to speak or fixes it to the morning.
The two ways the Daily Scrum goes wrong
The freedom to choose a structure does not mean every structure works. The common failure is the status meeting, in which each Developer reports upward and nobody adapts anything. That shape is attractive, because it looks orderly and hands a manager something to act on, and it quietly removes the reason the event exists.
The opposite failure is the event that runs long because the team starts solving the first problem it finds. Half the Developers then spend forty minutes on something that concerned two of them, which is the cost the timebox was there to prevent.
What the Daily Scrum does not replace
Developers talk to each other throughout the day, so the Daily Scrum confines none of that to one slot. The event also leaves Sprint Planning in place, since the plan it adapts is the one Sprint Planning produced. Detailed design and problem solving conversations often follow immediately afterwards with only the people involved, which the Guide describes as common and never requires.