CST waveguide port setting

Hi all,
what does the number mean in the mode setting in waveguide port setting.
And how to i define the number.

It a kinda old version but I am guessing this is representing the number of modes that will be excited during your simulation.
The solver in CST starts with checking which modes exists in your waveguide and numbers them according to ther cutoff frequency. So mode one would be the fundamental mode of the waveguide. Mode 2, the one with the lowest cutoff above the fundamental and so on. If you set this number to >= 1 you will also simulate the coupling between the modes.