What exactly is Ein Sof?

I’m not religious, I consider myself to be some weird type of agnostic, and I can respect and appreciate the parables and the symbols in most world religions. I’ve been looking further into Judaism lately, and I’m still a little stumped on the concept of Ein Sof. What is it? The formless version of God? Is it safe to say that Ein Sof is a way of articulating God’s essence as opposed to God’s characteristics? Please tell me the gist of what Ein Sof is! Thanks!