Flash memory, or Nand memory: Is what we call none volatile memory.
What it means is.
It does not require the memory chip to have a constant feed of electricity to retain the data stored on it, say when you unplug it from the computer once storing the data on it.
It is retained, until the data is overwritten by user intervention, data replaced or wiped, deleted from the device, by the user.
Where as volatile memory:
Requires a current to constantly keep and store the data that resides in it, cut the power and all is lost in volatile memory.
Flash memory comes under the section of none volatile memory due to this.
But still can ware out through lots of use in reading and writing data operations to the memory chip, mostly down to circuity degradation of the memory chip it`s self over long time, use or write or read operations preformed by the nand memory chip.
That is where it begins to fail to store the data on the memory chip.
As said all the data is set up as 1 or 0 on the usb pen drive,in what we call binary format.
What the core level of a Cpu works at in machine code, and understands.
All data is stored in this format, be it on a flash pen drive or the main system memory contained in a computer for data storage, or for an example the Hard disk drive of your computer. That may help your home work assignment ! Just kidding.