Period

Use a period (.) at the end of a declarative or imperative sentence.
• The meeting lasted for three hours. (declarative sentence)
• Return this video tape to the store. (imperative sentence)
Use a period after initials, abbreviations, and contracted words. (Abbreviations do not have internal spacing.)

• U.S.A. • A.A.R.P. • P.M. • Ms. • etc. • tsp.
Use only one period to complete a sentence which ends in an abbreviation.
• Fax the order to Harris and Son, Inc.
• My appointment is with Mark Siebold, M.D.
Use a period, rather than a question mark, after an indirect question or a courteous request.
• She asked what time you would be home. (indirect question)
• Could you please pass the mashed potatoes. (courteous request)