What is "upsherin"

Upsherin, Opsherin or Upsherinish ( Yiddish: אפשערן, lit. "shear off", Judaeo-Arabic: חלאקה, ḥalāqah) is a haircutting ceremony observed by a wide cross-section of Jews and is particularly popular in Haredi Jewish communities. It is typically held when a boy turns three years old. Among those who practice the upsherin, the male infant does not have his hair cut until this ceremony.