What is a lens?

The Last answer you had was terrible, if you would like a better one, you should be glad that i found this question.

Definitions of lens on the Web:

• a transparent optical device used to converge or diverge transmitted light and to form images
• genus of small erect or climbing herbs with pinnate leaves and small inconspicuous white flowers and small flattened pods: lentils
• (metaphor) a channel through which something can be seen or understood; "the writer is the lens through which history can be seen"
• biconvex transparent body situated behind the iris in the eye; its role (along with the cornea) is to focuses light on the retina
• electronic equipment that uses a magnetic or electric field in order to focus a beam of electrons

  recived from Wordnetweb.princeton.edu/perl/webwn