What a major pentatonic scale is
Major pentatonic uses scale degrees 1, 2, 3, 5, and 6. In C, that is C, D, E, G, and A: the sound of a major chord with two extra melodic notes.
Because it leaves out 4 and 7, the scale has fewer half-step tensions than the full major scale. That makes it useful for clear, singable melodies and simple fills.