Functionally, mods *are* plugins, and vice versa. The *only* distinction between the 2 is the platform people develop them on. Plugins are generally viewed from the Bukkit/Sponge world, mods from Forge. But, there is no difference in the purpose of them. Mods can go on a server, or a client. When you then take into account Sponge (which is both a Forge mod and a vanilla mod) uses the term plugin in, they are also acting like those "mods" you see as well.

A case can be made for the difference, provided that while they often have similar functions, the purposes can be very different.

Fair enough. Thanks for the consideration.

Mods and plugins are essentially the same in the end, so those will be long in the Modding subforum.