Monitor memory pressure (stress)
(Updated: )Memory pressure (stress) is an indicator of how much load your memory is experiencing at the moment. The higher the pressure, the less efficiently your memory processes data. To check memory pressure, open the Menu and look at the Memory monitor (or click the monitor and view Pressure).
Memory pressure status can be either normal or critical. A critical pressure warning indicates that memory has lost much of its efficiency.
To restore performance, close some of the running apps, especially those you're not using or the ones consuming the most RAM.