How does Excel shows error messages?

There are various kinds of errors in Excel that you will see. An error reference in a cell always starts with the # symbol. If the cell is a continuous line of them, it means the cell needs to be widened to show the value properly. Other than that, the # will be followed by a Word to indicate the specific error and will be followed the ! symbol. Some of the ones you may see are as follows, although there are many others:

#NUM!

#REF!

#DIV/0!

#NAME!

The help system will give you assistance on what can be the cause of the particular errors you come across.