When adding time in the program you will see the Private Description box and a checkbox option “Show private description on the invoice?”, which opens the Public Description box. The Private Description is the description that is required when entering time in the program, but the Public Description box is the one that actually shows on the invoice for the client to see. By default, the “Show private description on the invoice?” checkbox is always enabled below the Private Description, so typed into the Private Description will automatically copy into the Public Description.
The reason for this is if you would like to save a detailed description in the program but you might want the client to see only a portion of it. You would uncheck the “Show private description on the invoice?” box and re-type in the Public Description exactly what you want the client to see. This will allow you to keep two separate descriptions in the program.