PHP is one of the main website development languages and is used at the server side. It is a very powerful and increasingly popular programming tool. Facebook is developed in PHP, HuffingtonPost.com too, and many other large and complex but high-performance websites.
As for "PSD to HTML", it is an 'abridgement' for
"Conversion (also slicing) of digital images/designs which are prepared in Photoshop or other graphic packages and have such file extension as .PSD, .AI, .PNG into xHTML/CSS code as well as into WordPress themes and content management systems (Joomla, Drupal, etc) templates."
More about PSD to HTML you can read on our blog www.htmlcut.com/blog/welcome-to-a-psd-to-html-blog.html (it's a shameless self-promotion, sorry, but it's to the point, IMHO ), see also the video on Youtube youtube.com/watch?v=X2rqj6UFDZw.
php is an powerful tool nowadays for web development. it makes your website more dynamic and interactive. whereas psd is identifier for the file formats on the internet. while html is used in the past an easy way to develop your website. nowadays their are more powerful tools are utilized these days
PHP is the best programming language because its very easy to learn, and it is very flexible when coming to web creation. It's open-source, widely used, runs on different Operating Systems and Server platforms, and has built-in support for nearly every database around.
PHP is a scripted programming language that can be used to create websites. PSD is Photoshop's native file format. HTML is the "language" that web pages are written in - in fact, HTML stands for "hypertext mark-up language.