Buying in order to sell for profit is speculation. I completely and utterly agree that Steem, as well as many other blockchain techs, is very promising in this regard.

In*vesting* I believe originally means buying into a share of business. Share that implies the right to corresponding share in profits and assets possessed. One can argue that SP *kind of does* all that. The strange situation here is that Steem as a business has no external source of monetary income. All SP does, from economic point of view, is redistribution of 9.5% inflation of the same SP asset. SP is a share in business that has no profits by design.

There's also *lending*. Give someone money for a time, expecting them to return more, therefore enjoying profit. That's how SBD is supposed to work, but it currently does not.