The term "ballad" is misused a lot now anyway, as some will call any DT song that doesn't rock or prog out a ballad. For example, Along for the Ride is a song that is more mellow than not, but I wouldn't call it a ballad. Ballad usually are supposed to refer to slower love songs, not just any slower song.
I disagree with that. Nowadays it is associated with slow love song by many due to pop music, but the term ballad actually stems from a form of poetry with a sentimental/melancholic narrative (see definition). And that form of poetry set to music is also referred to as a ballad. I am no expert on this subject or anything, nor would I know what to call a ballad or not exactly. But as far as I am concerned, most slower love songs are ballads, but not all ballads are slower love songs.
But, as with all genre/classification discussions, a lot of it is highly subjective. And cultural, offcourse (especially since many languages have the word in some form, but possibly with slightly different meanings). And I maybe think the word is used in different ways (one way refers to the lyrical content, the other to the music itself?).