What does sister organization mean?

Could you please clarify the meaning of the term "sister organization"? Is it referring to two separate entities that share a close relationship or a common purpose, potentially collaborating on projects or initiatives? Or does it suggest a more formalized partnership or agreement between the organizations? Additionally, are there any legal or financial implications to being considered a sister organization? I'm curious to understand the full scope of this term and how it might impact the workings of these organizations.