A desktop application security audit is a systematic evaluation of a desktop application's security measures and protocols. Its aim is to identify vulnerabilities or weaknesses in the application's design, implementation, or operations that could potentially be exploited by cybercriminals, leading to unauthorized access, data breaches, or system failures.

In simpler terms, it's like a health checkup for your desktop application. The security audit examines your application to ensure it's safe from cyber threats. It helps you understand where your application might be vulnerable to attacks and how you can fix those vulnerabilities.

As for the activities involved in a desktop application security audit, they typically include:

1. Threat Modeling: This involves identifying potential threats and classifying them based on severity to understand the potential risks the application faces.

2. Static Analysis: Also known as 'code review', this involves examining the source code of the application to identify any security flaws or vulnerabilities.

3. Dynamic Analysis: This involves testing the application in real-time, often using automated tools, to identify security issues that may not be evident in the code but appear during operation.

4. Penetration Testing: In this step, testers act as attackers and attempt to exploit the identified vulnerabilities to understand their impact.

5. Post-Audit Review: After the audit, a detailed report is generated outlining the identified vulnerabilities, their severity, and recommended countermeasures or fixes.