Noun

(loci)

A place or locality, especially a centre of activity or the scene of a crime.

The cafeteria was the locus of activity.

(mathematics) The set of all points whose coordinates satisfy a given equation or condition.

A circle is the locus of points from which the distance to the center is a given value, the radius.

(genetics) A fixed position on a chromosome that may be occupied by one or more genes.

Noun

(en noun)

The person, place or thing from which something (information, goods, etc.) comes or is acquired.

* {{quote-book, year=2006, author=(Edwin Black)

, title=Internal Combustion, chapter=2 citation , passage=More than a mere source of Promethean sustenance to thwart the cold and cook one's meat, wood was quite simply mankind's first industrial and manufacturing fuel.}}

* {{quote-magazine, date=2013-07-06, volume=408, issue=8843, page=68, magazine=(The Economist)

, title= The rise of smart beta , passage=Investors face a quandary. Cash offers a return of virtually zero in many developed countries; government-bond yields may have risen in recent weeks but they are still unattractive. Equities have suffered two big bear markets since 2000 and are wobbling again. It is hardly surprising that pension funds, insurers and endowments are searching for new sources of return.}}

Spring; fountainhead; wellhead; any collection of water on or under the surface of the ground in which a stream originates.

* {{quote-magazine, date=2013-08-16, author= John Vidal

, volume=189, issue=10, page=8, magazine=(The Guardian Weekly) , title= Dams endanger ecology of Himalayas , passage=Most of the Himalayan rivers have been relatively untouched by dams near their sources . Now the two great Asian powers, India and China, are rushing to harness them as they cut through some of the world's deepest valleys.}}

A reporter's informant.

(computing) Source code.

(electronics) The name of one terminal of a field effect transistor (FET).