Seems to be silly, but is very informative. Many people in the world are ignorant about the true meaning of a flash drive & a pen drive & how to differentiate them. The differentiation of a pen drive & a flash drive appears to be complex for most people.
But the fact is that both these devices don't need any differentiation at all. It all depends on the manufacturers & the people. Yes, some people prefer to call their removable devices as flash drives whereas some other people prefer to call their removable storage as pen drives. The concept under these two names is the same i.e data storage.
Both these devices assist you in carrying your data wherever you go. One major technical difference between these two devices is that a pen drive is used basically as a removable USB storage device whereas a flash drive has many usages. One more difference is that a pen drive can be directly plugged into the USB port & the flash drive can even be accessible by a direct USB connection. The data in flash drives can even be stored inside a cellphone.
Both the Pen Drive & Flash Drive serve as your assistants who follow you along with your data. So, always use a pen drive/flash drive for your data backup & secure your data.