What exactly does Bootstrap, Series A, Series B, etc. mean?

On a website that hosts startups I saw these terms next to "funding":

• Bootstrapped
• Seed Round
• Series A
• Series B
• Series C

Can anyone please explain what exactly are all these terms?

I found a nice explanation here about Series A/Series B/Series C. But I did not manage to find some detailed information about "Bootstrapped" or other types of funding.

Bootstrapped : No funding from outside sources. Just using your own cash, sweat, and later on, revenue from customers.

Seed round : Early, high-risk investment. Usually from individual angel investors. This is generally before you get significant revenue i.e. before fully achieving product/market fit. It's money to build your product and iterate towards a point where you are ready to scale. High risk = expensive, so you have to lose proportionally more of your company in exchange for less money.

Series A/B/C : Institutional investment from VCs. Generally happens during growth phase when your idea is proven, you have significant traction with customers, you have achieved product/market fit and you need money to scale fast. This is lower risk (and progressively lower again for each later A/B/C/whatever round), so you generally give less of the company away.