An engagement pod on Instagram is a group of people who decide to like (and comment) on each other's content in order. Doing this sends a signal to the Instagram algorithm and help them be featured in the "Discover" section. This eventually brings more reach, visibility and new likes and followers.
Old engagement pods used to be done over Telegram and Instagram discussion groups. They worked but has many downsides. In 2020, engagement pods are automated. Automated engagement pods are much more efficient for multiple results:
Engagement pod automation should be done in a qualitative way: Rather than joining a huge pod with a lot of people outside of your usual audience, prefer joining an engagement pod where people are talking about the same topics than you do. First, because will be detected and taken into account by Instagram's scoring algorithm. Second, because you ultimately want your content to be seen by people in your niche, not just anyone.
Brands releasing content and obtaining very low like scores are not respected. Obviously, if the content is bad, engagement pods won't change anything much. But for new brands looking for an initial boost, engagement pods will give you that initial pool of likes and audience and get your name out there. If you're a small brand, try to have your friends, family, employees in the pod in order to make that boost as powerful as possible.