Hello;

Jog is a manual mode  you will use to position or test an axis, for example.

Fixed speed you will use for continuous running of your motor, on a motion profile or a speed control application.

Have a look at the following discussion, various expert members of this forum give their own descriptions on this issue:

https://support.industry.siemens.com/forum/ca/en/posts/jog-mode-or-fixed-frequency/146703

Hope this helps,

Daniel Chartier