We used to call them "expansion packs". They were the same thing as DLC, just without the DL. (Nobody had enough bandwidth to do large game asset downloads.)
Expansion packs or Addons came with a lot more high quality content with many more hours of actual gameplay content on a separate CD/DVD. The CD/DVD can be sold later.
Since 2006, a DLC is usually a minor content like a horse decoration, a car, a few short missions worth 1-2 hours gameplay, etc. DLCs come also with DRM, you cannot sell it later. (Also used in conjunction as pre-order bonus on e.g. Amazon or Steam) (Some still release Addons, some call Addons DLCs, but generally it is the way as described above.)
Since 2006, a DLC is usually a minor content like a horse decoration, a car, a few short missions worth 1-2 hours gameplay, etc. DLCs come also with DRM, you cannot sell it later. (Also used in conjunction as pre-order bonus on e.g. Amazon or Steam) (Some still release Addons, some call Addons DLCs, but generally it is the way as described above.)