Is ATMEGA328P the same as 16U2?
The 16u2 is related to the ATmega328p, and includes USB, but is more limited in resources.   While it would be possible to make an Arduino-type board from alone, this is unlikely to be what you have.

Rather, it is likely that you have a board with an ATmega328p as the main processor, and also a 16u2 which serves as a USB interface for it.

You could know for sure from what board type you select in the dropdown menu of the Arduino IDE.  If you are selecting something like "Uno" or "Duemilanove" you have a 328p as the main processor.

(The other presently common type of board is the "Leonardo" style where a 32u4 - essentially a bigger version of the 16u2 - is used as a single-chip solution that is both the primary processor and the USB interface.  But if that is what you had, it would not say 16u2 on it, unless it was an attempt to make a more limited "budget" version).