The technique is a cousin of wash-trading but focuses on the visible record rather than volume alone. A sequence of small upticks in a thin stock near the close, or coordinated prints on an alternative venue, can leave a chart that looks like accumulation.
It shows up most often in illiquid small caps, closed-end funds around net asset value publication, and in crypto pairs with fragmented liquidity. The related practice at the closing bell is marking-the-close.
Do not confuse it with legitimate activity that happens to be visible, such as an index fund buying in size at the close. The offence is the intent to deceive rather than the footprint itself.
Related: wash-trading, marking-the-close, market-manipulation, time-and-sales, pump-and-dump