What is a Web Designer?
Most simply put, a web designer is a rare kind of individual who is both creatively and technically minded, and then turns this talent to creating websites.
The term could be applied to a single person, or swapped out to refer to a web design company, or graphic design or advertising agency.
Web design is a professional occupation that requires specific skills, and just knowing HTML and CSS, how to put a page on The Internet, or publish a WordPress or Tumblr blog does not make you qualified.
A web designer is someone who can create beautifully stunning designs, but also make them usable, accessible to those with disabilities, and use specific design techniques within their designs to drive customers to action.
A web designer will think about how an end user (or customer) is going to interact with the page they're designing. People don't aimlessly browse to commercial websites. They usually go there with a purpose. A web designer does research and speaks to users to find out what that purpose is, and then designs the web page around it, making sure that not only is the page visually stunning as a whole, but that the visual design puts the user's goals front and centre, and doesn't get in their way.
Designing for the web is different than designing for any other medium.
The breadth of skills and experience required is sometimes daunting, yet the medium attracts designers from all spheres of design practice: from engineering and architecture, to product and graphic design.
Hiring a professional designer will usually save you money in the long run, as the product will be much better suited to its purpose, have greater longevity, and will ultimately make more money than one created by someone less professional or experienced.