Simply put, it is an acronym meaning Financial Independence, Retire Early.
This movement has gained traction among Millennials and it is a fairly popular financial topic in blogs, podcasts, etc. It is the act of living below your means. Ideally, paying off all expensive debt and saving as much of your paycheck as possible. It is achievable by increasing your income or decreasing your spending, make sure you have a budget too. Increase your income by learning a new skill or by adding a side-hustle; if you need inspiration, here is a post for you.
Reaching FIRE is a two-fold goal – become financially independent enough where you can retire without having to work. Many of those in the community focus mostly on become financially independent while the retiring portion is optional. Essentially the goal is to about flexibility, where you can do what you want when you want. As your job needs you more than you need it. It is about the ability to untether yourself from the 9-5, so you can work as much as you like.
For those of us on a low income, it seems like an unattainable goal, especially when realizing the high incomes of those within the community. It appears that the kind of frugality that is regularly experienced on a low income is elective for others. I have felt that way as I earn much less as a Ph.D. student. However, the goal is to accumulate enough assets that result in passive income, essentially 25 times your annual living expenses. Even if it takes a longer amount of time for those of us on lower-income to save to become financially independent, we will at least have built a nest egg.