It's an EA term - in TS2, they were referred to by EA as Chance Cards regularly. They resembled these, but only appeared in careers. If you've played the Political Career, an example is the popup to steal campaign funds. In TS2, a Sim had two options (eg "Steal" or "Don't Steal") plus an option to ignore. Ignoring did nothing. When a Sim picked an option, there was a 50/50 chance (roughly) to get a good or bad result. A certain reward increased it to 80/20. So, for instance, this could happen:
Sim chooses to Steal. Good result. Sim gets $5000.
Sim chooses to Steal. Bad result. Sim loses job.
Sim chooses not to Steal. Good result. Sim gets 2 Logic Points.
Sim chooses not to Steal. Bad result. Sim's relationship with a random Sim goes down.