Transliteration is the practice of converting a text from one writing system into another in a systematic way. In the library word is it used to describe non-Roman characters into Roman alphabet. You will find how to transcribe Persian letters into English in Persian Transliteration Table.
This link is to the scanned text of the 1997 edition of the "ALA-LC
Romanization Tables: Transliteration Schemes for Non-Roman Scripts,"
approved by the Library of Congress and the American Library
Association. These tables were developed for use when the consistent
transliteration of non-Roman script (e.g. Persian) into the Roman
alphabet is needed, for example, in order to catalog non-Roman
materials.