Private placements skip the public marketing process. In exchange the buyer receives restricted securities that cannot be freely sold until a registration statement covers them or a holding period passes. That restriction is what justifies the discount the buyer negotiates.
For public shareholders the placement is dilution that arrives without a bookbuild and often on terms they would not have been offered. The structure ranges from plain stock to convertible preferred to a toxic-convertible that reprices downward as the stock falls.
Example: a company sells 5M restricted shares at $8 when the stock trades at $9.60, a 17% discount reflecting a six-month lockup on resale. The buyer's implied compensation for illiquidity is $8M of instant paper gain.
Related: pipe-deal, restricted-stock, dilution, toxic-convertible, form-144