This phrase is an allusion to Mr. Justice Douglas's majority opinion in
Griswold v. Connecticut wherein he uses the idea of
penumbras and
emanations coming out of the text of the
Constitution, particularly the
First Amendment,
Third Amendment,
Fourth Amendment,
Fifth Amendment, and
Ninth Amendment in the
Bill of Rights to develop the idea of a
right to privacy.
Drawing on all of these amendments, he concludes that "from the totality of the constitutional scheme under which we live" the right of privacy is a fundamental personal right.
For example, he argues that in the third amendment, it is not the action of quartering troops in a home that is prohibited, but instead the idea of an unrightful invasion of privacy.
The Ninth Amendment in particular is useful in that it reminds people that there are rights that exist outside the constitution that still deserve protection. But people are probably more familiar with the Fifth Amendment's Self-Incrimination Clause. This clause "enables the citizen to create a zone of privacy which government may not force him to surrender to his detriment." (Griswold v. Connecticut)