What is “The Enlightenment”

Immanuel Kant answered that it consists of “humankind’s emergence from its self-incurred immaturity,” its “lazy and cowardly” submission to the “dogmas and formulas” of religious or political authority. Enlightenment’s motto, he proclaimed, is “Dare to understand!” and its foundational demand is freedom of thought and speech. “One age cannot conclude a pact that would prevent succeeding ages from extending their insights, increasing their knowledge, and purging their errors. That would be a crime against human nature, whose proper destiny lies precisely in such progress.”

A 21st-century statement of the same idea may be found in the physicist David Deutsch’s defense of enlightenment, The Beginning of Infinity. Deutsch argues that if we dare to understand, progress is possible in all fields, scientific, political, and moral: Optimism (in the sense that I have advocated) is the theory that all failures—all evils—are due to insufficient knowledge …. Problems are inevitable, because our knowledge will always be infinitely far from complete. Some problems are hard, but it is a mistake to confuse hard problems with problems unlikely to be solved. Problems are soluble, and each particular evil is a problem that can be solved. An optimistic civilization is open and not afraid to innovate, and is based on traditions of criticism. Its institutions keep improving, and the most important knowledge that they embody is knowledge of how to detect and eliminate errors.
Quoted from and properly attributed in: Enlightenment Now, by Steven Pinker 

BRITANNICA:
Enlightenment, French siècle des Lumières (literally “century of the Enlightened”), German Aufklärung, a European intellectual movement of the 17th and 18th centuries in which ideas concerning God, reason, nature, and humanity were synthesized into a worldview that gained wide assent in the West and that instigated revolutionary developments in art, philosophy, and politics. Central to Enlightenment thought were the use and celebration of reason, the power by which humans understand the universe and improve their own condition. The goals of rational humanity were considered to be knowledge, freedom, and happiness.