In essence, homelessness means that you don't have a home and because of this you are living on the streets.

in 在这里是介词，表示"在...方面"或"就...而言"。 essence 来自拉丁语 essentia（存在），指"本质、实质、精髓"。 in essence 是一个固定短语，意思是"本质上、实质上"，用于强调事物的根本性质或核心特征。