nginx 配置文件里server_name为_是什么意思？

Question

这个东西真不是很明白，别人都说这个是来反向代理的，可是怎么体现的，还有这个配置文件，是怎么样一个操作过程能讲下么，真的不明白，知道的非常零散，

Default server configuration

#
server {
listen 80 default_server;//这个是默认监听端口号 80 可是谁监听谁，nginx监听电脑上的80端口么
listen [::]:80 default_server;

# SSL configuration   
#
# listen 443 ssl default_server;
# listen [::]:443 ssl default_server;
#
# Note: You should disable gzip for SSL traffic.
# See: https://bugs.debian.org/773332
#
# Read up on ssl_ciphers to ensure a secure configuration.
# See: https://bugs.debian.org/765782
#
# Self signed certs generated by the ssl-cert package
# Don't use them in a production server!
#
# include snippets/snakeoil.conf;

root /var/www/html;  //这个好像是我如果写一个静态网页可以在这个路径下写然后在环回地址显示，，具体是什么不明白求解释

# Add index.php to the list if you are using PHP
index index.html index.htm index.nginx-debian.html;//不明白 就是一堆html文件

server_name _;//也不明白  别人说配的域名 

location / {
    # First attempt to serve request as file, then
    # as directory, then fall back to displaying a 404.
    try_files $uri $uri/ =404;
}//普通定位 但是也不明白 nginx去定位什么，

# pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
#
location ~ \.php$ {
    include snippets/fastcgi-php.conf;

    # With php7.0-cgi alone:
    #fastcgi_pass 127.0.0.1:9000;
    # With php7.0-fpm:
    fastcgi_pass unix:/run/php/php7.0-fpm.sock;
} //正则匹配如果后缀是php网页就进行php解析么，

# deny access to .htaccess files, if Apache's document root
# concurs with nginx's one
#
#location ~ /\.ht {
#    deny all;
#}

}
请稍微详细解释下，非常感谢大佬们啦，，，，，

Answer 1

人家问的是 server_name 值为 _ 下划线什么什么意思， 都瞎nm装逼。
谁知道回答一下，我也等着呢