Diagnostics is the process of figuring out what's wrong with something by examining it carefully and running tests. When your computer won't start, a technician runs diagnostics to identify the problem. When you feel sick, your doctor uses diagnostics like taking your temperature, listening to your breathing, or ordering blood tests to determine what's causing your symptoms.

A mechanic uses diagnostics to understand why a car is making strange noises. An engineer uses diagnostics to discover why a bridge has cracks. Teachers sometimes use diagnostic tests at the beginning of the year to figure out what each student already knows and what they need to learn.

Think of diagnostics as detective work. Instead of guessing randomly, you gather clues systematically. A computer might run diagnostic software that checks each part of its system one by one. A doctor might order diagnostic imaging like an X-ray to see inside your body. The goal is always the same: to understand the problem accurately so you can fix it effectively. Good diagnostics saves time and prevents mistakes, whether you're troubleshooting a video game console or figuring out why your science experiment didn't work as expected.