There's usually a legal distinction. Blocking does require looking at the request, but the accept/request decision is made instantaneously and is usually based on a static blacklist (or whitelist). It doesn't necessarily require logging.
Monitoring usually means logging all activity and then automatically or manually sifting through the logs to look for things, possibly much later, and possibly in response to other subsequent events.
Monitoring is considered by most people to be worse, and may come with more legal liabilities.
