One example is the military retirement. It could be called a 2.5% A fund, because multiplying years of service (generally 20) by 2.5% = 50%. This means that for the rest of your life, you'll receive half of what you made during your highest-paid three years on active duty. If you work until 25 years, 25 * 2.5% = 62.5%. For civilian companies there's generally a "fully vested" point where your percentage will not go up anymore no matter how long you work.