PCI
Peripheral Component Interconnect, local bus used on Pentium systems that runs at 33 MHz.
PHP
PHP: Hypertext Preprocessor, PHP is an HTML-embedded scripting language. Much of its syntax is borrowed from C, Java and Perl with a couple of unique PHP-specific features thrown in.
When a PHP file is requested by a client/browser over the internet the host server will run the PHP script and will generate HTML code as output or process data that is sumbited.
The goal of the language is to allow web developers to write dynamically generated pages quickly.
For more information visit the PHP website.
PSU
Power Supply Unit or also known as a computer's switched mode power supply unit converts110-240 V AC power from the mains supply, to several output both positive (and historically negative) DC voltages in the range 12V to 3.3V. Modern PSU's will be an ATX form factor and older PSU's being AT.