This video discusses the AC and DC vertical coupling modes on an oscilloscope. It shows that these settings are not really the same thing as the AC/DC settings on a multimeter, but rather they dictate how the signal is coupled to the vertical channel of the scope. In many cases, the DC coupling mode is very useful for looking at AC signals. Similiarly, the AC coupling mode can be very useful when looking at DC signals. The choice of which vertical coupling mode to use depends upon the signals and circuits that you are looking at.