per

Per is defined as to, for, by or according to.

(preposition)

An example of per used as a preposition is in the phrase, "as per standards," which means by the standards.

Per mean for each once.

(adverb)

An example of per used as an adverb is in the phrase, "one cookie per person," which means one cookie for each person.

See per in Webster's New World College Dictionary

through; by; by means of
1. for each; for every: fifty cents per yard
2. during each: used in indicating a rate of motion or activity: to cover 500 miles per day
according to: used esp. in business: per your instructions

Origin: L < IE base *per-, a going beyond > far, for

through, throughout: perfoliate, peroral
thoroughly, completely, very: perfervid
Chem.
1. containing a specified element or radical in its maximum, or a relatively high, valence: perchloric acid
2. containing the maximum amount of the indicated element: perfluoropropane (completely fluorinated propane, CF)
3. containing the divalent group O: peracid
  sometimes peroxy-

Origin: L < per, through: see per

See per in American Heritage Dictionary 4

preposition

To, for, or by each; for every: Gasoline once cost 40 cents per gallon.
According to; by: Changes were made to the manuscript per the author's instructions.
By means of; through.

adverb
Informal