Defect Density
// Definition
Defects per unit of size — typically per thousand lines of code or per function point. Useful for spotting unusually buggy modules and tracking quality trends over time, with the usual caveats about goal-induced metric gaming.
// Related terms
Defect Leakage
The ratio of defects found in production to total defects (production + pre-release). Measures how well testing caught bugs before users did. Lower is better.
Code Coverage
The percentage of source-code lines, branches, or statements executed during a test run. A useful but easy-to-game metric — high coverage doesn't guarantee good tests.
Bug Lifecycle
The stages a defect passes through from discovery to closure: New → Assigned → In Progress → Fixed → Verified → Closed (with possible Reopened, Deferred, or Rejected branches).
Learn more · Manual Software Testing
Chapter 1 · Lesson 4: Building Your Testing Intuition Over Time