"Extreme frugality" means the practice of being extremely careful with money and being very thrifty in order to save as much as possible. Full definition
Many FIRE bloggers focus on maximizing their savings rate at their current incomes, living extremely frugally, and planning a lifestyle that will allow for extreme frugality for years to come. (thecollegeinvestor.com)
Before they began their excursion into extreme frugality, while they were enjoying $ 120 haircuts and $ 200 restaurant meals, the couple was already saving between 40 % and 50 % of their after - tax income (and that doesn't even count maxed - out 401 (k) contributions and mortgage principal!). (getrichslowly.org)
Yes, there are people making $ 40k that are retiring early, but to get there they need to practice the kind of extreme frugality that has no appeal to the average person. (themoneycommando.com)