1) Period 2) Punctuation mark 3) Road safety maneuver 
In punctuation, the full stop (in British English) or period (in American English) is the punctuation mark placed at the end of a sentence. The full stop glyph is sometimes called a baseline dot because, typographically, it is a dot on the baseline. This term distinguishes the baseline dot from the interpunct (a raised dot). The full stop glyph is...
(period) Punctuation mark which indicates: 1
A change in aperture or shutter speed that admits half as much or twice as much light
A change in aperture or shutter speed that admits half as much or twice as much light. 
a punctuation mark indicating the end of a sentence
Punctuation mark (.). It has two functions: to mark the end of a sentence and to indicate that a word has been abbreviated (see abbreviation). It is also used in mathematics to indicate decimals and is then called a point
period (defs. 10, 11).