(Latin: through, across, over; beyond, by means of)

Per ardua ad astra.
Through difficulties to the stars.

Motto of the Royal Air Force, U.K.

Per aspera ad astra. (Latin motto)
Through adversity to the stars.

Motto of the Canadian Air Force.

per aspera belli (Latin motto)
Through the hardships of war.
per capita (adverb)
A reference to each person (by the head): "The city has budgeted a financial amount for pupils per capita annually for educational expenses."
per cent
Another spelling for percent.
per centum, per cent
By the hundred.
per diem (s) (noun, per diems (pl)
An amount or allowance of so much for each day.
Per lumen scientiae viam invenient populi. (Latin motto)
Translation: "Through the light of knowledge the people will find a way."

Motto of Texas College, Tyler, Texas, USA.

per mensem
By the month.
per mille
per os; P.O.; p.o.
Through the mouth.

A pharmaceutical instruction for the administration of medicine.

per procurationem
By proxy [substitution].

It means, "proxy vote, by authorization." In some situations, it is also expressed as per procuratorem.

Per scientiam ad salutem publicam.
Through knowledge to public health.

Motto of Johns Hopkins School of Hygiene and Public Health, Baltimore, Maryland, USA.

per se
Per viritatem vis.
Strength through truth.

Motto of Washington University, St. Louis, Missouri, USA.