9. What is the purpose of HTTP headers and how do they influence web communication?

HTTP headers are a core part of HTTP requests and responses, carrying crucial information about the client's request and the server's response. They include metadata such as content type, content length, server type, and more.

There are several types of HTTP headers:

1. General headers: Apply to both requests and responses, but not to the content itself.
2. Request headers: Contain more information about the resource to be fetched or about the client itself.
3. Response headers: Hold additional information about the server's response, like its location or about the server itself.
4. Entity headers: Contain information about the body of the resource, like its content length or MIME type.

HTTP headers influence caching, security, the control of data transmission, and content negotiation. For example, the Cache-Control header can dictate how a resource should be cached by browsers, while the Content-Security-Policy header helps mitigate certain types of attacks like XSS by specifying which dynamic resources are allowed to load.