A term often used in BDSM circles but may be in other chat communities.
The idea is that when you are meeting a cyber-date you will have a friend
waiting for your phone call and if you do not make that call on time then that
person will call the police and sic 'em on the person you were supposed to be
Obviously, this is useless unless you know a great deal of real life information
about the person you are meeting and have some reason to trust that that information
Thankfully, the fuzz are not too quick to go kicking in doors on the say-so
of someone who is 5 states away because their online friend is 45 minutes late
for a phone call.
While there may be some merit to the use of a safe-call as a deterrent there
is no guarantee that this would slow down a rapist or serial killer at all...
so you probably don't want to rely on this.
Interestingly, when the topic comes up on many BDSM mailing lists it turns
out that many BDSM couples never used one. Amazingly, it seems a majority
of those people who seem to push safe-calls most strenuously didn't use them.