I have checked Google translate and leo.de. However, I wasn't able to discern the difference between the two words, because both seem to translate generically to committee. What is the difference between Ausschuss and Gremium?
Ausschuss is possibly best matched by subcommittee: a group elects a subgroup to deal with a special topic. Currently well known due to press coverage are the Untersuchungsausschüsse from the German Bundestag.
A gremium ist just a sort of established group: examples are standardization groups, where industry chooses the delegates, Mitbestimmungsgremien like pupil parent association, representation of the workforce in companies and many more.
Summarized: any Ausschuss is also a Gremium, but not vice versa.