Pam is a diminutive of Pamela. Pamela originates in Greek language and was invented by Sir Philip Sidney for a character in his epic prose The Countess of Pembroke's Arcadia. Later on, it was used by Samuel Richardson for a character in his epistolary novel Pamela, or Virtue Rewarded, first published in 1740. Since then, Pamela has been used regularly as a feminine given name. Lately, its usage has declined in the United States.