The Cyrillic letter Er was derived from the Greek letter Rho (Ρ ρ). It has no connection to the Latin letter P (P p), which evolved from the Greek letter Pi (Π π), despite both having the same form.

The name of Er in the Early Cyrillic alphabet was рьци (rĭci), meaning "speak".^[1]

In the Cyrillic numeral system, er had a value of 100.

The Cyrillic letter Er (Р р) looks similar to the Greek letter Rho (Ρ ρ), and the same as the Latin letter P (П in Cyrillic).

As used in the alphabets of various languages, р represents the following sounds:

• alveolar trill /r/, like the "rolled" sound in the Scottish pronunciation of ⟨r⟩ in "curd"
• palatalized alveolar trill /rʲ/

The pronunciations shown in the table are the primary ones for each language; for details consult the articles on the languages.

• Ρ ρ/ϱ : Greek letter rho
• R r : Latin letter R
• P p : Latin letter P
• ₽ : Russian ruble sign
• П п : Cyrillic letter П
• Я я : Cyrillic letter Я

•   The dictionary definition of Р at Wiktionary
•   The dictionary definition of р at Wiktionary