The difference between an email client and webmail client
An email client is a program that is used to access email. Email clients can be located either locally on a computer or on the internet (clients based on the internet are known as "webmail clients").
An email client typically provides more options for mail management than a webmail client, and also has the ability to work offline. Common email clients include Outlook, Apple Mail, and Thunderbird.
A webmail client allows you to access your mail from anywhere, requiring only an internet browser. Common webmail clients include AtMail, SquirrelMail, Gmail, Hotmail, and Yahoo Mail.