What represents 1 bit?

An infinity of representations of 1 bit are possible. A few of them are
- the digits 1 and/or 0
- amount of charge
- polarity of charge
- signal strength
- signal frequency deviation
- signal polarity
- magnetic field direction
- magnetic field strength
- signal phase
- modulation depth
- reflectivity
- presence of a conductive path
- duration of a signal
- interval between signals
- interval between signal changes
- ...
Several of these may be in use for a given information bit within a modern computer.