What do you mean by Great Communication

I am no swinger. I actually jumped on Reddit hoping to find relationship advice and how to make it work long term. I landed here because I guess Swinger couples are truly built differently because you are basically participating openly in sex outside your marriage without having a problem with it. And reading through the a lot of the comments, I realize that you all talk about boundaries and Communications that makes your relationship work.

When you say Great Communication, what exactly does that entail? Please give me some pointers.