The question simply doesn't make sense. Any periodic function has both period and frequency- given one, you can calculate the other.
Neither "represents" an orbit.
If you do have something, such as a planet, orbiting, then you must have both a period (the number of days, seconds, etc. required to complete one full orbit) and a frequency (the number of orbits per day, second, etc.) and one is just the reciprocal of the other. If you are thinking of one as "representing" the orbit, the other could as well.
To answer the question you DIDN'T ask but probably intended, it is more common to give the period of an orbit of a planet about the sun rather than the frequency just because it is a simpler number in the most common units.
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