The Main Differences
A mobile website is a specialized version of your current website that is optimized for your smart phone or mobile device. Since smart phones have smaller screens and are touch-based devices, having a version specifically for mobile devices will give your users a much better browsing experience. Mobile websites can be accessed on multiple mobile platforms (such as iPhone, Android, Blackberry, etc.) because only a web browser is required to access the mobile website.

A mobile app is a software application that you download (from the App Store or Android Market) and install on your mobile device. A mobile app can be practically anything from a calendar, a video game, an online bank account manager and even a website. Mobile apps have to be written specifically for a mobile device platform. For example, an iPhone mobile app will not work on an Android phone and vice versa.

Which one do you need? Do you need both?
With smart phones becoming more affordable and wireless speeds getting faster, having an alternative mobile website is eventually going to be the norm. The main reason is because of usability and speed. Normal websites are designed for use with larger screens and a mouse/keyboard. They are also created with faster Internet connections in mind. Mobile websites take advantage of the smaller screen and touch-based nature of the device making navigation and browsing much easier and faster. They also require the file sizes of the images and other website content to be smaller for faster downloads  from Oyun Club Net.

However some websites might have special features that would make more sense as a mobile app or might only work as a mobile app. Types of websites such as an e-commerce website or bank websites are good examples. Take for example Chase (m.chase.com). You can log into your account online using their mobile website to access your account or you can download the Chase mobile app. Are both really necessary? In this case I would have to say yes. I tried accessing my bank account using both methods and here are the results from this quick test:

Mobile Website:

Pros: Accessible through any web browser on any mobile device, don't need to download/install anything
Cons: Slower, less responsive. Have to use web browser to navigate there first (or use bookmarks). Can't use built-in camera to take pictures for deposits.
Mobile App:
Pros: If used frequently, much easier and faster to use, requires single tap to access (after installed). More responsive because of native device code. Takes advantage of built in camera to make deposits.
Cons: Must download and install first. App must be written and approved for specific device(s).