What is the auto-fill feature called ?

Hi there,

I have a spreadsheet where i am populating the email id for my students. I have manuelly typed the email id column for two rows. But when type the third row, excel automatically recognize the pattern of my email id, and populating values for all my rest of the blank rows.

What is the feature is called ? i want to understand how it is generating the records so i can explore if i can populate the values without using the formulas. Please help.

Screen shot below :