So in the 10002 event the terms used are 'read' and 'write'. But in the gossip client we ignore that and use this instead:

READ - where you actually read from

INBOX - where you tell others you read from

WRITE - where you actually write to

OUTBOX - where you tell others you write to

One example of why there is a difference: maybe you want to read from a popular relay to not miss anything, but you don't want to advertise to others that you want them to put your stuff on that popular relay.