The effect was used infrequently until Innistrad block when it saw a noticeable increase.
The term 'mill' originated with the card Millstone, which originally had the text ' :Take the top two cards of target player's library and place them in target player's graveyard.' As more cards were printed with the 'put X cards from a player's library into their graveyard' effect, players began to call it 'milling', and the term became accepted informally even by Wizards R&D.
