A: Adiabatic compression means no heat crosses the system boundary (Q=0), while isentropic is a subset of adiabatic where entropy also remains constant (S1=S2) and efficiency is 100% — meaning all isentropic processes are adiabatic, but not all adiabatic processes are isentropic. In practice, the problem statement will typically tell you which process applies, and if not, the available given information will limit which equations you can use.