In the Heathen movements, a kindred is a local worship group and organisational unit. Other terms used are hearth, theod (only within the Theodish movement), blotgroup, sippe, and other less popular ones such as garth, stead, and others.
Kindreds are usually grassroots groups which may or may not be affiliated with a national organization like the American Asatru Folk Assembly, the Ásatrú Alliance, The Troth, rather than the Swedish Forn Sed Assembly or the Odinic Rite. It is more typical for a kindred to not be affiliated to any organization within the US than elsewhere.
Kindreds are often composed of hearths or families as well as individuals, and the members of a kindred may be related by blood or marriage, or may be unrelated. The kindred often functions as a combination of extended family and religious group. Membership is managed by the assent of the group.
My time as a Heathen has been marked mostly as a solo practitioner. I tried joining a kindred about a year or so ago (might be two), but the local one had fallen apart and I never heard back from anyone.
Kindreds, however, are important. Heathenism is, at its base level, about family as much as it is about heroics or individuality. A lot of rituals in Heathenism kinda require more than one person, so it becomes important to have enough members to perform them. Not to mention, having a support structure that works almost like a family is a nice thing to have. No doubt, in the future, kindreds may become important in ways we do not realize.