A highpass filter usually refers to an EQ (equalizer).
It's when you set it at a certain frequency, say, 40 Hz, and let all frequencies above 40Hz "pass through" or go uneffected, but all frequencies below 40Hz get dropped down in level (a slope).
Audition has 2 equalizers. The graphic and parametric. I usually use the parametric EQ as it gives more control. But you may want to work with the graphic one for awhile until you get the hang of it.
The only benefit is if your track needs a highpass. It's common to do a highpass at about 20 Hz as that will get rid of a lot of low end "rumble" and can even give you a little more headroom.