I know the difference between the two, but what does it mean when there's both? Like for example on lddb.com, it shows the movie Assassins as both CLV and CAV. What does that mean?

It's usually because it's a multidisc movie, and the majority of the side's are CLV with one being CAV. Usually the CAV side is reserved for either the climax of the movie or for special features.

For example, Lost Highway has one disc that is completely CLV, but because the movie was longer than two hours it needed to be on three sides. Probably because the remainder of the movie was under 30 mins. (the max. time limit of a CAV disc), they decided to make that 3rd side in CAV. I have seen movies where all three sides are CLV, usually with each side totalling about 45 mins.

Another example is Goldeneye, in which the movie is spread across two discs. 3 of the 4 sides contain the movie in CLV, in which the third side contains the last few minutes of the movie plus a special making-of documentary for the rest of the side. The fourth side is in CAV and contains the rest of the special features.

+CAV means only the LAST side is CAV.
CLV/CAV means it's a mix of both.

Julien