On Thursday, Rav Michel Twerski spoke to the entire yeshiva about the three different types of forgiveness that we ask for, "Slach lanu, machal lanu, caper lanu."  As explained to me, the message was that Teshuva is more than asking a father for forgiveness for doing something wrong.  Rather, when we sin, we do three things. We create a negative force,  make ourselves crooked, and due to the principle of aveirah gorerres aveirah, we set out on the path of sin which naturally leads to more sins.  The three terminologies in the tefilla (slach, machal, and caper) are an attempt to correct these three different problems.