A MEAN stack developer is a professional who specializes in building web applications using the MEAN stack, which stands for MongoDB, ExpressJS, AngularJS, and Node.js. The MEAN stack is a collection of JavaScript technologies that are widely used for developing robust and scalable web applications.

As a MEAN stack developer, you will be responsible for designing and implementing the backend and frontend components of web applications, ensuring seamless integration between them. You will also be responsible for writing efficient and optimized code, debugging and troubleshooting issues, and ensuring that the application is scalable and reliable.

Some of the key responsibilities of a MEAN stack developer include:
- Developing server-side logic using Node.js and ExpressJS
- Designing and developing APIs for seamless communication between the frontend and backend
- Designing and developing the frontend using AngularJS or other relevant frameworks
- Designing and implementing database structures using MongoDB
- Ensuring that the application is optimized for maximum speed and scalability
- Debugging and troubleshooting issues as they arise
- Collaborating with other developers, designers, and stakeholders to ensure that the application meets business requirements.

To be a successful MEAN stack developer, you should have a strong understanding of JavaScript, web development principles, and modern web development frameworks. You should also have experience with designing and implementing APIs, working with databases, and debugging and troubleshooting issues. Additionally, you should be able to work collaboratively in a team environment, have excellent communication skills, and be able to work under tight deadlines.