meaning of scenario in yii with example

hello all,

        i am new in yii i need to know what is the meaning of scenario with its full description and example

From,

jalpa patel

See links below:

http://www.yiiframework.com/wiki/266/understanding-scenarios

http://www.yiiframework.com/doc/guide/1.1/en/form.model#triggering-validation

http://www.yiiframework.com/doc/guide/1.1/en/form.model#declaring-validation-rules