A password is an operator option for certain functions. One may program in whatever character pattern is desired to allow access to whatever function is needing protection.
In some systems it takes an engineer to do it by repinning a program plug, in others anyone may do it from the CDU keyboard.
In the company I'm now working for, one of our pilots did it to five aircraft in three days and almost grounded the fleet until we figured out what the hell happened to cause the "Maint Check" symbol to appear.
TWA had a password to keep stick actuators from getting into the maintenance pages. Some companies have passwords to guard the updated databases so that only duly authorized individuals may do the changeover.