What is Private Placement?

Legal Definition
Private placement (or non-public offering) is a funding round of securities which are sold not through a public offering, but rather through a private offering, mostly to a small number of chosen investors.

PIPE (Private Investment in Public Equity) deals are one type of private placement. SEDA (Standby Equity Distribution Agreement) is also a form of private placement. They are often a cheaper source of capital than a public offering.
-- Wikipedia
Legal Definition
A debt not registered with the securities regulator. It is sold on a ceveat emptor basis to only experienced investors. It is illiquid and only transfers to a short list of buyers. This can only be done when laws permit. Refer to safe harbor rule, public