Both Uses

Puritans
in
All's Well That Ends Well, by Shakespeare
(Auto-generated)

If men could be contented to be what they are, there were no fear in marriage; for young Charbon the puritan and old Poysam the papist, howsome'er their hearts are severed in religion, their heads are both one; they may joll horns together like any deer i' the herd.†
Scene 1.3

Puritan = an English Protestant who in the 16th and 17th centuries who wanted simpler worship and strict, hard-working lives
—Though honesty be no puritan, yet it will do no hurt; it will wear the surplice of humility over the black gown of a big heart.†
Scene 1.3 *

Definitions:

(1) (Puritans)
English Protestants in the 16th and 17th centuries who wanted simpler, “purer” worship and emphasized hard work over pleasure

Protestants are Christian groups that broke away from the Catholic Church; in the United States, well-known Protestant churches include Baptists, Methodists, Presbyterians, and Episcopalians.
(2) (meaning too rare to warrant focus)
As a common noun (not capitalized unless at the start of a sentence), puritan or puritanical can refer to someone who is very strict -- especially about religious principles or proper behavior.