Unweighted vs. weighted
Unweighted high school GPA uses a simple 4.0 scale with no bonuses for honors, AP, or IB. A in any class equals 4.0. This is what most high school transcripts report as the "official" GPA.
Weighted GPA adds bonuses for course difficulty, see /weighted for the 5.0 calculator. Many colleges look at both numbers when evaluating applications.