Manipulation includes placing orders you intend to cancel to move price (spoofing), trading with yourself to fake volume (wash trading), and spreading false information to move a stock (pump-and-dump). Regulators pursue it in stocks, futures, and increasingly in crypto.
For a trader, the practical lesson is that visible order-book size and social-media enthusiasm are both easy to fake.
Example: a group coordinates online to buy a thin stock and post fabricated news, then sells into the spike. Participants have been prosecuted by the sec for exactly this.
Related: spoofing, pump-and-dump, sec, cftc