Brief me on this topic

Walking into a conversation about something you do not know.

Brief me on this topic in under 400 words. Cover what it is, what the live arguments are, and what a newcomer usually gets wrong. Assume I am clever and know nothing. Flag anything where the field has moved recently, or where you are not confident the picture is current.

Topic:

Starting on a new topic. Mapping an unfamiliar field, scoping the question, and finding somewhere real to begin reading.