Concave and convex are two basic types of lenses. A convex lens focuses light rays, whereas a concave lens causes the light rays to diverge.

Wife is a man’s partner in marriage. Mistress is a woman who has a continuing extramarital sexual relationship with a man.

Though Wikipedia and WikiLeaks are non-profit organizations, they function totally differently, that is, Wikipedia is a free online informative encyclopedia, whereas WikiLeaks is a free publishing online site...

Lover is a person who is in romantic relationship with another person. Mistress is a woman who has an extramarital relationship with a married man.

Wiki is a collaborative website, which can be edited, updated and deleted by its relevant users, while a Blog is a personal website usually created by an individual to share information.