There has been a couple of really good definitions of "parish mission", as heard by two different priests.
Fr. William Casey calls it a "crash course on Catholicism". When I heard Fr. Casey mention this the other day, it made me think of two years ago, when I heard Fr. Anthony Mancini call it "the classroom of Christ".
Both priests I just mentioned put on excellent missions. Fr. Mancini is known in these parts for his music. He directs the Gregorian Concert Choir, the resident professional choir at the Cathedral of SS. Peter and Paul in Providence, RI. He became Cathedral music director upon the retirement of Alexander Peloquin in 1990, and was appointed Cathedral rector just a couple of years ago. But little did I know until 2004 how well he preaches.
Fathers Casey and Mancini have been my two favorite priests that I've heard a mission from, not only in my 25 years as a church organist, but in the 41 years I've been on this earth.
So, perhaps, collectively - a "crash course on Catholicism in the classroom of Christ"?