In the latest TEM training a threat is an event or situation outside the influence of the flight crew but needs management by the flight crew to maintain safety margins. They can include latent conditions but generally are more immediate issues.
Here is a (non - exhaustive) list of threats (hazards) experienced by airline crews on a daily basis.
ATC Threats
Challenging instructions / ATC errors
Language difficulties
Heavy traffic
TCAS events
Environmental Threats
Adverse WX
Terrain
Airport Conditions
Aircraft Threats
Dispatch deviations / MELs
Malfunctions
Automation events / anomalies
Crew Support Threats
Dispatch events / errors
Ground crew events / errors
Maintenance events / errors
Operational Threats
Time Pressures
Irregular Operations
Radio congestion / poor reception
Cabin Threats
Passenger events (e.g. unruly pax)
Cabin events
Flight attendant errors
As I said the list is not exhaustive.
Best wishes
PJ