Scrum, is an empiricism-based Agile framework, that handles complex and complicated scenarios, with an iterative and incremental approach, over the traditional, sequential (Waterfall) approach of software development. It's a set of values, roles, events, and artifacts that are easy to understand and tough to master, and gives a practical set of tools for operating in accordance with Agile values and principles, to deliver valuable products that match the criteria set for them ("Done") in short iterations (typically less than 4 weeks).
You can liken it to the tactical level of a large strategic offensive, e.g. in WWII, the Brécourt Manor Assault (made famous by being featured in the award-winning HBO mini-series "Band Of Brothers") was part of a much larger D-Day landing at Normandy, and was led by Richard Winters.
With minimal instructions of "There's fire along that hedgerow there. Take care of it," and no briefing, Winters found himself given the task of destroying a German artillery battery, with a numerically inferior force, of 12 men, fighting against 60 German soldiers, which he completed successfully, and which was later used as a "textbook" example of such an assault. There was little knowledge of the layout beforehand, and a lot of the decisions had to be taken on the spot to achieve the set goal of "taking care of it".
The reason it's relevant, is we're often facing uncertain conditions, as part of a much larger goal for a company. We know we want to "create the world's most user-friendly CMS" or "become the most popular e-commerce platform for SMBs", etc. but the concrete implementation is then delegated down to the individual teams, who, if properly trained, can self-organize to solve smaller packages of work, which coalesce into larger things later on, and all contribute to the realization of 1 massive goal, of the aspirational nature - the ever elusive product vision.
However, unlike an army, which practices what we might call "Management 1.0", development teams aren't led by commanders and are punished for their disobedience by jail or even a firing squad (of the literal sense, seeing as how the prospect of being fired/terminated for a poorly done job looms over most of us).
Instead, given the understanding that software implementation of such ambitious goals, in an ever-changing world, is anything BUT predictable, teams are taught to self-organize, work in sprints, hold demos for stakeholders, and retrospectives for the team members. The Scrum Master facilitates the process, the Product Owner prioritizes the backlog and refines the user stories and everything works smoothly, that is, until you scale up. Now there are 2 teams, 3, 4, or 10. The organization grows and it assigns department managers and team leads to organize work, and deliver the value it expects, gather communication into shorter and succinct messages.
Taking Scrum from the individual team level, up to a scalable solution isn't an easy task, but there are proven paths of how you could do that effectively and efficiently.