As best as I can describe:

Point Beyond: Purchasing a ticket to a destination connecting through your desired city and not using the connecting flight. SFO-DEN-COS and not going on the COS instead of purchasing a SFO-DEN ticket that would more than likely cost more.

Throw Away: Purchasing a round trip ticket but only using the outbound portion.

Back to Back: Purchasing two round trip tickets that include Saturday Stayovers. Use the outbound from both tickets. If you had two trips to the same city say Monday to Thursday both weeks. One ticket would be from your originating city on the first Monday and the return would be on the second Thursday. The other ticket would originate in your Desination City on the first Thursday and the return would be on the second Monday. This gives you two tickets that appear to have Saturday Stayovers but in reality you do not stay over the Saturday in your destination city at all.

Don't really know the difference between Hidden City and Point Beyond Tix. Maybe someone else can help?

I hope this long winded response has answered your question.