The Internet Printing Protocol (IPP) is defined in RFC2910 and RFC2911. It's an extendable protocol, for example ‘IPP Everywhere’ is a candidate for a standard in mobile and cloud printing and IPP extensions for 3D printing have been released.
Because IPP is based on HTTP, it inherits all existing security features like basic/digest authentication and SSL/TLS encryption. To submit a print job or to retrieve status information from the printer, an HTTP POST request is sent to the IPP server listening on port 631/tcp. A famous open-source IPP implementation is CUPS, which is the default printing system in many Linux distributions and OS X. Similar to LPD, IPP is a channel to deploy the actual data to be printed and can be abused as a carrier for malicious PostScript or PJL files.