Web design we refer to here is the asthetics point of view which is the customer-facing part of the website. A web designer is concerned with how a site looks and how the customers interact with it. Good web designers know how to put together the principles of design to create a site that looks great. They also understand about usability and how to create a site that customers want to navigate around in because it’s so easy to do.
Web development we are refering to is the application aspect like how the site reacts to clicking of the a button, forms, calculations, logic and also the back-end of the website, the programming and interactions on the pages. A web developer focuses on how a site works and how the customers get things done on it. Good web developers know how to program CGI and scripts like PHP, Java etc. They understand about how web forms work and can keep a site running effectively.