Proxy Server:
A proxy server is an intermediary server that acts as a gateway between a client computer and the internet. It receives requests from clients seeking resources from other servers and forwards those requests on behalf of the client. The proxy server can modify the client's request or response, cache data, and provide additional security and privacy features.

External Access:
One of the primary uses of a proxy server is to provide external access to a computer or a local network. When a client device connects to the internet through a proxy server, the server acts as the client's representative, making requests and receiving responses on its behalf. This allows the client to access resources on the internet indirectly, hiding its own IP address and location.

Advantages of External Access:
1. Improved Security: By acting as an intermediary, the proxy server can add an extra layer of security by filtering malicious traffic, blocking harmful websites, and protecting against cyber threats.
2. Anonymity and Privacy: The proxy server hides the client's IP address, making it difficult for websites or other entities to track the client's online activities. This helps maintain anonymity and privacy.
3. Content Filtering: Proxy servers can be configured to filter content based on predefined rules. This allows organizations to restrict access to specific websites or types of content, ensuring compliance with company policies or legal requirements.
4. Bandwidth Optimization: Proxy servers can cache frequently accessed resources, reducing the need to fetch them from the original server. This helps to optimize bandwidth usage and improve the overall network performance.

Other Uses of Proxy Servers:
While external access is a common use case, proxy servers can also serve other purposes such as:

1. Backup: Proxy servers can act as backup servers for other servers or services. They can store copies of resources and serve them when the original server is unavailable or experiencing issues.
2. File Handling: Proxy servers can handle file transfers between clients and servers, optimizing the process and managing resources efficiently.
3. User Permissions: Proxy servers can be used to control and manage user permissions, allowing or denying access to specific resources based on user credentials or other factors.

Overall, a proxy server primarily functions as a computer with external access, providing an intermediary connection between clients and the internet while offering various benefits such as improved security, anonymity, content filtering, and bandwidth optimization.