Definition
Agile means "nimble." It's a way of working, and a philosophy, where instead of planning everything perfectly up front and building for a long stretch, you build quickly in short cycles, test as you go, and flexibly change direction.
Instead of memorizing the whole map, you turn on GPS
In the past, software was built the way houses are built. Teams spent months writing a thick, hundreds-of-pages blueprint. Then they built everything in the exact order on the page, and only showed users the finished product at the very end. Because the work flows in one direction, like water falling down a cliff, this is called the "Waterfall model."
But in the software world, users' tastes change fast, and new technology pours out every day. Say you spend a whole year building exactly to plan. Then you launch, and users say, "This isn't what I wanted." All that effort goes down the drain.
Agile was created to prevent that kind of waste. Instead of deciding every turn before you leave, you put out a small, working product quickly. Then you watch how real users react and keep adjusting your compass in real time to head the right way.
Show a little finished work every few weeks
Many Agile teams, especially ones using Scrum, work in short cycles of about one to four weeks. Each short development cycle is called a "sprint" (or an iteration). At the end of every sprint, the team shows something that actually works and gets feedback. The goal is for that result to be ready to ship right away.
Say you're building a new food delivery app. You wouldn't try to finish payments, reviews, points, and coupons all at once over a year. First you'd build and launch a very simple version where people can browse a menu and tap a call button. Then you'd watch what users really want.
If users want payments first, you build payments in the next sprint. If they ask for recommendations, you build that first. By repeating fast releases and continuous feedback over and over, you grow the product smarter step by step.
To be more precise: it doesn't mean no planning
To be more precise, Agile is absolutely not "skipping the plan and winging it." Instead of clinging blindly to a plan, you review and update it far more often as things change.
Agile also isn't one fixed set of rules or a piece of software. It's closer to a work philosophy and set of values: communicate well, and don't be afraid of change. That's why a variety of specific methods are used to put the philosophy into practice.
The best-known example is "Scrum," which bundles rules like sprints, defined roles, and retrospective meetings. The "daily scrum" is just one piece of it. The team meets at the same time every day for 15 minutes to check whether they're on track for the sprint goal and adjust the day's plan. It's often held standing up, so it's also called a stand-up. Another popular method is "Kanban," which shows your work as cards on a board. In the end, the heart of Agile isn't going as fast as possible. It's the flexibility to change direction quickly as things change.
Common misconceptions
Agile means skipping planning and documentation and just building as fast as possible.
Agile doesn't ignore plans or documents. It cuts back on excessive paperwork that becomes useless when things change, and it values working results and flexible plan updates more.
Where you meet it
When launching a new app, you release it with just one core feature instead of finishing everything, then update it every week.
As a team, you regularly try out what you've built so far and revise your plan for what to improve next week.
In one sentence
Instead of planning everything perfectly up front, Agile means building fast in short cycles, getting feedback, and flexibly adjusting as you go.