Is it normal for my hz to keep changing?

[Carl81]

Playing rage 2 .
My display setting is 2560 x 1440p and 144hz .

I noticed that when i click on the monitor joystick it shows certain stats . When im not moving in game it shows as being 144hz ...when im driving round or what ever it changes.
Some numbers are random .
Could be 121hz or 104hz .
Is this normal?
Ive taken a pic to show the stat.
I have a rtx 2080 super and i have the gigabyte Ad27qd monitor . Am using the display cable that came with the monitor.
Am i being thick here?

thanks

 

[bagel]

that'll be the g-sync, matches refresh rate to fps so you don't get tearing

 

[Randomface74]

Variable refresh rate lol

 

[random_matt]

Hz does change if a scene or whatever becomes more demanding, it's fine.