When you first open a spreadsheet, you will notice it looks like a grid with columns and rows. This grid is called a worksheet. 

There can be more than one worksheet within a spreadsheet file. By default, when you open a Google Spreadsheet, you are shown one worksheet, but have the ability to add more. This might be necessary if you work as a teacher using a spreadsheet to keep track of students – you might add a new worksheet for each student or subject you teach. 

The default name of the worksheet is Sheet 1 and you can see it at the bottom of the screen. To help you identify content, you have the ability to change the name of the sheet(s). This comes in handy if you have more than one worksheet in your spreadsheet file.