During the festival parade, many people will march in disguise.

disguise 是名词，来自动词 disguise（伪装、掩饰），前缀 dis- 表示"去除"，词根 guise 来自古法语，意思是"外表、装扮"。disguise 合起来指"改变外表以隐藏真实身份"，即"伪装、乔装"。