Direct answer: Progressive overload is gradually increasing the demand of training for load, repetitions, useful sets, amplitude, control or more difficult variations. Register performance and only advance when the technique and effort are within the planned. Without registration, it is easy to confuse fatigue with progress.
The Double Progression Method
Choose a range, for example 8 to 12 repetitions. Keep the load until you reach the top with technique and expected margin in all sets. Then increase the weight little and return to the lower part of the range.
Other ways of making progress
Amplitude
Run more useful amplitude with control.
Stability
Reduce compensation and repeat trajectory.
Volume
Add sets only when recovery allows.
Difficulty
Use unilateral variation or better resistance.
Why the cargo can stay the same
Menstrual cycle, sleep, stress and schedule change performance. Maintaining load with better technique is also progress. Evaluate week trends, not a bad session.
When to do deload
If performance falls for several sessions, pain and fatigue accumulate and motivation plummets, a week with less volume or load can recover capacity. Deload is tool, not mandatory calendar.