Wiktionary
n. A letter written by one person who is familiar with another, usually a teacher, employer, or person of similar authority, evaluate and often extolling the fitness of the other person for a position.
Wikipedia
Usage examples of "letter of recommendation".
Armed with Palli’s letter of recommendation, they instead arranged exchanges for fresh horses at local town chapters of the Daughter’s Order.
Armed with Pallis letter of recommendation, they instead arranged exchanges for fresh horses at local town chapters of the Daughters Order.
And you can just tear up that letter of recommendation I wrote for your snivelling, little son for Acquisition University because I'll disavow all knowledge of its existence!
And when I had become invaluable I had no trouble in getting a very good letter of recommendation, to anybody whom it might concern, from the curator, who was a well-known man in his field.
After three months he one day asked me to give him a letter of recommendation to my old friend Sheik Ali bin Salim, the Lewali of the Coast, at Mombasa, for he had seen him in my house and now, he said, he wished to go and work for him.