THE STOP that comes at the end of a sentence or of any other complete statement has been called point, elliptical for full (or perfect) point; full (or complete) pause; full stop; period. The second is obsolete; the first, obsolescent. Of the other two, period and full stop, the former is preferred by most scholars and printers, the latter by most other people. Nobody will go to heaven for using period, nor to hell for using full stop.
A period is so named because it comes at the end of a period, strictly of a periodic sentence, but now loosely apprehended as any sentence, even if it consists of only one word, e.g. 'Yes', elliptical for 'Yes, that is so', 'Yes, I will', etc. Compare the modern catchword 'Period': indicating the end, not only of a statement, a telegram, a letter, but also of a holiday, an indulgence, a permission, and so forth. Compare also Chaucer's 'And there a point, for ended is my tale'.
Full stop virtually explains itself: a full stop, like a full or perfect point, is obviously not an imperfect point or stop, whether as brief as a comma or as clear-cut as a semicolon or as disruptive as a dash or as smooth as a pair of parentheses or as culturedly poised as a colon: here ends the statement, here ends the sentence. The etymology of period is helpful, as etymology so often is. Period, French période, Latin periodus, Greek periodos (peri, around+hodos, a way, a road), means literally a going round, hence a rounding off, especially as applied to time, more especially still the time represented by a breathing. At the end of a breathing, a sentence, a statement, one pauses to take breath, either because one must or because it is convenient to do so. This explains why the elocutionary term pause and, for the full stop, full pause were formerly used as synonymous with (full) point or (full) stop.
The one indispensable stop is the full stop. In most simple sentences-those containing one verb-this stop suffices. In the following examples, only an over-punctuator would increase the punctuation:
He went home early that day.
He could hardly have done anything else.