Web development means the development of web pages over a domain. The development can take place on two networks either internet(public) or intranet(private).
Web development is a very broad field, it ranges from static text to e-commerce websites and from client scripting to network security. Millions of operations come under Web development hence web development demands intellect along with innovation so that one's product can differ from the million others. Web development is all about how distinguished and optimized one's product is from others.
A website is a set of web pages which are accessed from a single domain with the purpose of providing information about a particular person or topic. Creating websites is known as Website Designing and Development.
Mobile application is application software made to run on smart-phones, tablets and various other electronic devices to produce various results ranging from games to calendars. The process of creating mobile applications is known as mobile application development.
Purpose of mobile applications varies a lot, from specific development for a client to development for the whole market. User specific applications are purely based on the needs of the client that is what all operations it wants from the application.