testimonial
noun [ C ] uk/ˌtes.tɪˈməʊ.ni.əl/ us/ˌtes.təˈmoʊ.ni.əl/
证明信，介绍信
a statement about the character or qualities of someone or something
formal or old-fashioned（以前雇主写的）推荐书
a formal written description of someone's character and qualities given by a previous employer