Microsoft Office Excel completes text entries that you start to type in a column of data — if the first few letters that you type match an existing entry in that column. If you want to stop automatic completion, you can turn this option off.
In Excel 2016, 2013, and 2010 versions: Click File > Options.
In Excel 2007: Click the Microsoft Office Button , and then click Excel Options.
Click Advanced, and then under Editing options, select or clear the Enable AutoComplete for cell values check box to turn this option on or off.