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!)
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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"!