The Nancy Reagan defense is a tactic in corporate finance used to counter a takeover or merger bidder who has made a formal bid to shareholders to buy their shares.
When the board of directors of the target company meets to consider the bid, they "just say no."
For example, in a discussion of a takeover of the Walt Disney Company by Comcast, analyst Andy Kessler on Wall Street Week stated "there are two great Wall Street defenses.
"[1] An early use of the term referred to NCR's takeover defense against AT&T in 1991.
[2] The term refers to the "Just Say No" anti-drug campaign of the early 1980s and repeated by former United States First Lady Nancy Reagan advocating abstinence from recreational drug use.