100 (or one hundred) is the natural number that comes after 99 and before 101.

Basic meaning

In everyday language, “100” usually just means the quantity one hundred:

  • 100 items, 100 dollars, 100 people, etc.
  • It is also written as the Roman numeral C.

In math and science

  • 100 is 10210^2102, the square of 10.
  • It is the basis of percentages (“per centum” = “by the hundred”), so 100% means a complete or full amount.
  • In the metric system, 100 centimetres = 1 metre.
  • In chemistry, 100 is the atomic number of fermium (Fm) , a synthetic radioactive element.

In culture and slang

  • The 💯 emoji (“100 points”) comes from perfect test scores (100 out of 100) and is often used to mean “100% real” or “keep it 100” (fully honest).
  • In casual speech, saying “that’s 100” can mean something is completely true, genuine, or excellent.

If you tell me what context you saw “100” in (math, money, slang, temperature, etc.), I can tailor the explanation more precisely.