httpd_accel_host
This directive enables HTTP server acceleration (see Chapter
15) and HTTP interception (see Chapter 9). When Squid is configured for
server acceleration, this directive specifies the hostname or IP
address of the backend server. When used in an interception
configuration, you should probably use the keyword virtual here.
When this directive is set, Squid disables ICP and rejects proxy-HTTP requests unless you also enable httpd_accel_with_proxy.