What does the far Left mean by "open borders"?

I don't mean the right wing, strawman argument that Biden or Obama supported "open borders". I'm looking for people on the far left to describe what they mean when they sincerely advocate for an open border policy. Meaning: the free movement of people between jurisdictions with little or no restrictions.

I'm not looking to argue just to better understand this POV. What would this look like for the USA in practice, and what would be the major implications?

Edit: because people are saying that no one on the left supports "open borders". The prompt for this question was seeing plenty of "No Borders" signs at a protest on the way to work. Sure, it is a fringe view, but some faction of the left does advocate for this position.