These are basically synonymous in terms that if you are looking to have Web work to be performed by a business or freelancer.
The reason for this is because there are very few designers or developers/programmers that do not do both. It is tough for a legitimate company and to offer only one and not the other. Many times the term "website design" is preferred by those that do both because it is a more common term and speaks to the fact that what most clients seek is a great look-and feel. (This is probably because this is what a client can see – most clients never see the backend code or databases.) But the above does not mean that these companies are not great at building CMS-driven, dynamic, user-friendly sites, just because the company doing the work claims to primary be a “website design” company.
But if you wish to recognize a difference, here it is:
Website design = the frontend = graphics and layout that give a look and feel
Website development/programming = the backend, including PHP, HTML, SQL, etc.
To speak to the claim that “website design” is the most common term, here are the Google numbers of results for searches:
· website design 230,000,000
· website development 161,000,000
· website programming 45,400,000
· website designer 325,000,000
· website developer 45,200,000
· website programmer 16,900,000
Source: http://seattlenewmedia.com