What is "Tempo"?

Tempo is referring to the 'time under tension' for a specific movement or muscle group.
(there are many examples of this; 21X0, 1010, 3010.......to name a few.)

⁃ THE FIRST NUMBER is lowering the load to the bottom of the movement.  For example, if a back squat is rx’d at 30X0, it means that from the top of the movement, you should take 3 seconds (1 one thousand, 2 one thousand, etc.) to reach the end point of the exercise (full depth for the squat). So, the first number signifies the lowering portion of ANY exercise.

⁃ THE SECOND NUMBER represents the pause, if any, at the bottom of the movement. Because this example (30X0) says 0, it means that it is simply 3 seconds down, 0 pause, and then back up. If the tempo was 31X0, then you would have to pause for 1 second at the bottom of the movement. If it was 32X0, then you would have to pause for 2 seconds, and so on.

⁃ THE THIRD NUMBER is raising the load to the top of the movement. When it says “X” as the third number, it means to 'accelerate' the load as fast as possible – regardless of how fast the weight is actually moving, intention to 'accelerate' is most important. If the number is 2020, as sometimes rx’d for GHD sit-ups or back extensions, then you have to take 2 seconds to lower fully, 0 pause in the full stretch position, then take 2 seconds to come back to the top (you are capable of going faster, but that is not what is being asked, so follow the numbers), with 0 sec rest before going into the next rep.

⁃THE FINAL NUMBER represents the pause, if any, at the top of movement. If it says 30X1 for a weighted pull-up, then you have to hold your chin over the bar for one second before lowering for 3 seconds to full arm extension.

Also, you have to LEARN to read the number, then apply it to the given
exercise. Chin-ups, for example, are a special case - there are other examples as well (i.e. deadlift). Chin-ups begin with the raising portion first, not like a back squat or bench press. So, if the tempo is 30X0, the first thing you look for is NOT the 3 second prescription, but the X, meaning that you begin with the third number for this exercise, not the first one.