A threat model is a list of the most probable threats to your security and privacy endeavors. Since it’s impossible to protect yourself against every attack(er), you should focus on the most probable threats. In computer security, a threat is an event that could undermine your efforts to stay private and secure.
Focusing on the threats that matter to you narrows down your thinking about the protection you need, so you can choose the tools that are right for the job.
To identify what could happen to the things you value and determine from whom you need to protect them, you should answer these five questions: What do I want to protect? Who do I want to protect it from? How likely is it that I will need to protect it? How bad are the consequences if I fail? How much trouble am I willing to go through to try to prevent potential consequences?