Some terms have an unofficial but widely known meaning in Magic jargon. For example, a "cantrip" is a spell that lets you draw a card, and a "bear" is a vanilla 2/2 (with "vanilla" having its own meaning!)
The canonical name for these seems to be 'Mana Rocks', probably so named after one of the very first, Fellwar Stone.
"Mana Rocks" might be a genuine term, but I don't think it's a particularly useful one, as it's not very descriptive of the use of these cards.
If I was talking about this class of card, in a way more likely to explain why I'd want to include some in my decks, I'd just go for "artifact-based mana acceleration". I know this answers your question less well than Steven's answer, but on the other hand I, and I'm sure many others, would never use the term "mana rocks"!