Is sister company a legal term?

Excuse me, I'm just wondering, when we hear the phrase "sister company," is that actually a legal term that carries a specific meaning in the world of business and finance? Or is it more of a colloquial way to describe two companies that have some sort of close relationship or connection, but not necessarily any formal legal ties? I'm curious to know if there's a clear definition for it in the legal sense, and if so, what exactly does it entail?