What does it mean to "finalize" in Julia?

I can't speak for CUDArt, but here is what finalize means in Julia: when the garbage collector detects that the program can no longer access the object, then it will run the finalizer, and then collect (free) the object. Note that the garbage collector can still access the object, even though the program cannot.

Here is an example:

julia> type X
           a
       end
julia> j = X(1)  # create new X(1) object, accessible as j
julia> finalizer(j, println)  # print the object when it's finalized
julia> gc()      # suggest garbage collection; nothing happens
julia> j = 0     # now the original object is no longer accessible by the program
julia> gc()      # suggest carbage collection
X(1)             # object was collected... and finalizer was run

This is useful so that external resources (such as file handles or malloced memory) are freed if an object is collected.