I saw the following question on a CAT from another test prep company:

If a fair six-sided die is rolled three times, what are the odds that neither a 2 nor a 4 will show up on any roll?

Answer: 8/27

I thought that "the odds" is defined differently than "the probability." Should I assume these two terms are synonomous on the GMAT? Perhaps this test prep company doesn't recognize that these two terms have different definitions. Or, perhaps the GMAT considers them to be equivalent.

You're absolutely right, zzzzzz. "Odds" is not synonymous with "probability".

The term "odds" won't show up on the GMAT (at least not without a definition).

The term is typically used by gamblers as a way of labeling sports bets. Saying "the odds are 1-to-4 that X will happen" means that the probability that X will happen is 1/(1+4)=1/5. In the example you cited, 8/27 is the probability. The odds would be 8-to-19. The person who wrote the question simply made a mistake.

But don't worry - the real GMAT question writers use words correctly, and "odds" is not a word that you'll have to deal with on the GMAT.