Here is an interesting cell format that disappears whatever the text you enter..
Step:1. Select any cell and then click on Format cells dialogue launcher as in the below screen shot (Ctrl + 1 is the keyboard shortcut to invoke Format Cells dialogue)

Step: 2. Select “Custom” in the Category box. Select any arbitrary format style in the Type options. The selected format style will now be available for editing in the Type text box as in the below screenshot.

Step: 3. Now change the format style to three consecutive semi-colons (;;;) and then click OK as below. If there is already any content, it becomes invisible from the cell. If any new content is entered, it also becomes invisible, once pressed Enter.

Explanation: Usually cell format takes the below semi-colon separated sytax (full four part syntax):
PositiveNumberFormat; NegativeNumberFormat; ZeroFormat; TextFormat
Since nothing is entered for each of these formats, nothing will be visible in the cell even after entering any contents into the cell.
Remember that this is just the format of cell content and the actual content does not disappear. This is evident when viewed the cell contents from the formula bar or when entered into cell edit mode as can be seen below (see the contents of cell B4 in the cell as well as in the formula bar):

Hope you enjoyed this one.. please do share your comments, questions, compliments..if any.. Have happy time until my next blog.. 🙂