Web design 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 is 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. They understand about how web forms work and can keep a site running effectively.
SEO stands for “search engine optimization.” It is the process of getting traffic from the “free,” “organic,” “editorial” or “natural” listings on search engines. All major search engines such as Google, Yahoo and Bing have such results, where web pages and other content such as videos or local listings are shown and ranked based on what the search engine considers most relevant to users. Payment isn’t involved, as it is with paid search ads.