Repsonsive Design means making your service/app friendly on all platforms and devices. Users are 45% more likely to use a repsonsive website.
Cascading Style Sheets is a style sheet language used for describing the presentation of a document written in a markup language like HTML.
Hypertext Markup Language is the standard markup language for documents designed to be displayed in a web browser.
SQL is used to communicate with a database. According to ANSI, it is the standard language for relational database management systems.
PHP is a server-side general-purpose programming language originally designed for web development. Many things can be done in PHP.