What does *Scepter Upgradable* mean?

A lot of skills have different effects under this Scepter Upgradable condition. I'm new to the game, and I don't know what this means.

For instance, the Venomancer's Poison Nova reads the following:
SCEPTER UPGRADABLE: Increases damage and duration, and decreases cooldown.

Solution 1:

If an Ultimate is "Scepter Upgradable", that means purchasing the Aghanim's Scepter item will enhance your hero's ultimate. Usually there is a damage increase, cooldown decrease, and/or mana cost decrease, although some heroes have additional enhancements (i.e. Tiny with a scepter will wield a tree that enhances his Toss damage and gives him cleave damage for his regular attacks).

Aghanim's can be assembled with a Point Booster (you can get this at the Secret Shop), a Blade of Alacrity, an Ogre Axe, and a Wizard Staff.

Total Cost: 4200

While there is a limited amount of heroes whose Ultimates are enhanced by Aghanim's, IceFrog has previously stated that he wishes to implement scepter upgrades for all heroes.

Solution 2:

This indicates that these abilities can be enhanced if carrying the item Aghanim's Scepter.