Opsec is also used in the context of personal information on the Internet.
"friendly actions" is one's personal life, especially name, age, relatives, and whether one is currently home, at work, at school, visiting relatives, on vacation, etc.
"enemy intelligence" is the presumed hackers looking for personal information they can use to either scam or impersonate someone.
It's generally good form to be aware of whether the personal information one shares publicly on the internet can be used to harm oneself or others by strangers with bad intent.
And to be clear, anything that is visible without logging in (or by using a free account) is continually and as-good-as-permanently in public.