Full explanation
Bootstrapping means growing your company without raising money from investors. You start small, sell to real customers fast, and reinvest the profits.
It forces discipline. You cannot afford to build features nobody wants. Every euro spent has to come back.
Bootstrapped startups grow slower but founders keep full control and 100% of the company.
Concrete example
You launch a SaaS at 19€ per month, get 50 customers in 4 months, and use the 950€ in monthly revenue to pay for hosting and ads. You never raised a single euro.