Also known as queerplatonic partnerships, these are committed intimate relationships which are not inherently romantic or sexual in nature. They may differ from close friendship by having more explicit commitment, status, and structure, similar to a conventional romantic relationship - but ultimately the differences and similarities are determiend by those involved. Just like other relationship types, they can consist of a single couple or a group of individuals.
And while this is common within them, it is not only for the aro and ace communities! You can have a queerplatonic relationship regardless of your romantic or sexual orientation.