Also, sorry, I was taking terminology from the GP. The real term for this is cross-correlation—with autocorrelation being the application of the above operation

Also, sorry, I was taking terminology from the GP. The real term for this is cross-correlation—with autocorrelation being the application of the above operation onto a single function; i.e., taking ac(f(t), g(t)) as defined above, the autocorrelation of g is really defined to be ac(g(t), g(t)).