A client connects to the Proxy Server, requesting some service, including connection, a file, web page, or other resource accessible from another server and the request is evaluated by the proxy server as a means to simplify and restrain its sophistication….

Proxies were devised to add encapsulation and construction to distributed systems. Now, most proxies are internet proxies, providing anonymity and easing access to content on the Internet.

Open proxies

An open proxy is a forwarding proxy server that’s accessible by any Internet user. An An anonymous proxy that is open enables users to hide their IP address using other Internet services or while browsing the Web. There are varying levels of anonymity yet, including several processes of ‘fooling’ the customer into revealing itself regardless of the proxy used.

Reverse proxies

A reverse proxy forwarding them to servers in an internal network and requiring requests from the Internet. Those making requests may not know about the internal network and connect to the proxy.

A reverse proxy (or surrogate) is a proxy server that seems to clients to be an average server. Requests are forwarded. The reply from the proxy server is returned if it came straight from the first server, leaving no knowledge of the source servers to the client. Reverse proxies are installed in the area of one or more web servers. Using “inverse” originates in its counterpart “forward proxy” since the reverse proxy sits nearer to the web server and functions only a limited set of sites. There are several motives for installing inverse proxy servers:

Load balancing: the load can be distributed by the reverse proxy to several web servers, each web server serving its own program area. In this kind of situation, the reverse proxy may have to rewrite the URLs in each web page.
Function/cache static content: The web servers can be offloaded by a reverse proxy by caching static content like images and other graphical content that is static.
Compression: the proxy server can optimize and compress the content to accelerate the load time.
This particularly gains dynamically created pages.
Security: the proxy server can shield against some OS and Web Server special strikes and is an added level of defense. Nevertheless, it will not provide any protection from assaults against the web application or service itself, which is usually considered the bigger risk.
Extranet Publishing: a reverse proxy server while keeping the servers behind the firewalls facing the Internet can be used to convey to a firewall server internal to an organization, supplying extranet access to some functions. Security measures should be considered to shield the remainder of your infrastructure in case this server is endangered, as its web application is exposed to attack from the Internet if used in this manner.

Source