To regress means to go backward or return to an earlier, often less advanced state. When scientists notice a patient's health regressing, they mean the person is getting worse instead of better. When a student who was reading chapter books suddenly struggles with simple sentences, teachers might say their skills have regressed.

A broken bone that was healing might regress if the patient doesn't follow a doctor's orders. A country's economy can regress during hard times, losing ground it had gained.

You might also hear about regression in psychology. Sometimes when people face stress or big changes, they temporarily regress to behaviors from when they were younger. A six-year-old starting at a new school might regress to thumb-sucking for comfort, even though they had stopped years earlier.

In math, regression has a special technical meaning related to finding patterns in data, but in everyday conversation, regress usually just means moving backward instead of forward. While progress means improvement and advancement, regress is its opposite: losing ground, sliding backward, or returning to a state you had moved beyond.