.

The full stop (Commonwealth English), period (North American English), or full point . is a punctuation mark used for several purposes, most often to mark the end of a declarative sentence (as distinguished from a question or exclamation).
A full stop is frequently used at the end of word abbreviations—in British usage, primarily truncations such as Rev., but not after contractions which retain the final letter such as Revd; in American English, it is used in both cases. It may be placed after an initial letter used to abbreviate a word. It is often placed after each individual letter in initialisms, (e.g., "U.S."), but not usually in those that are acronyms ("NATO)".