What is an Issue Log?
The issue log tracks problems that have already happened and need resolution: each issue gets an owner, a priority, a target date, and a status. It's the project's active to-do list of obstacles — reviewed at every status meeting until each item closes.
The exam distinction that matters: a risk is uncertain and lives in the risk register; an issue is certain — it already occurred — and lives here. When a risk materializes, it graduates from the register to the issue log.
Worked example
"Vendor API sandbox is down" enters the issue log Monday: owner — integration lead; priority — high; action — escalate to vendor account manager; target — Wednesday. It isn't a maybe. It's blocking two developers right now, and the log is what keeps it from being forgotten by Friday.