A pixel is a smallest addressable element in the display of a mobile device.
Though the term pixel may be used in various contexts. eg- camera image pixel, pixel in photo print, pixel per inch etc
In context of an image, a pixel is smallest single component of an image.
Megapixel (MP) means a million pixels. The term is used in image to represent the elements in an image. The term also reflects the number of image sensor elements in a mobile camera image sensor.
For example a pixel Resolution of 4920 x 3264 (ie. 16,058,880) indicates 16 MP.