For those unfamiliar with the concept of pinned chats/messages, basically this means that whatever message or chat that you want is pinned at the top of the screen, meaning that no matter how many other chats pop up, that particular chat will always remain at the top. If you do chat with a lot of people and don’t want to have certain threads lost, then this is a useful feature to have.
According to The Android Soul, it appears that chat pinning will work for both individual and group chats. It will also work with up to 3 threads at once, but we’re not sure if there are plans to add more in the future, although we guess having too many might defeat the purpose of pinning chats in the first place.
We’re not sure when the feature will be made available to all WhatsApp users (including iOS), but as it stands it is available in the beta so hopefully it won’t be too long.