[http] What is HTTP "Host" header?

Given that the TCP connection is already established when the HTTP request is sent, the IP address and port are implicitly known -- a TCP connection is an IP + Port.

So, why do we need the Host header? Is this only needed for the case where there are multiple hosts mapped to the IP address implied in the TCP connection?

This question is related to http http-headers

The answer is

I would always recommend going to the authoritative source when trying to understand the meaning and purpose of HTTP headers.

The "Host" header field in a request provides the host and port
information from the target URI, enabling the origin server to
distinguish among resources while servicing requests for multiple
host names on a single IP address.