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 notes of a C major triad plus two smooth melodic tones.
Because it omits 4 and 7, the scale avoids the strongest half-step tensions in the major scale. It does not replace the full major scale, but it is a dependable source of consonant notes for major-key bass lines.