The terms major and minor are used to identify the combination of a pattern of tones that make up a scale. In Western music, a scale is made up of eight pitches, with the first and eighth being one octave apart in pitch.
To visualize the changes between pitches as one changes notes in a scale, think of a piano keyboard. The difference in sound between any two immediately adjacent keys is called one half-step. This means that the difference in sound between a white key and the black key right next to it is one half-step. The difference in sound between keys that have one key between them is called one whole step.
A major scale follows a pattern of having whole step intervals between the first and second, second and third, fourth and fifth, fifth and sixth, and sixth and seventh pitches. A major scale uses a one-half step change in pitch between the third and fourth pitches and between the seventh and eighth pitch, the octave from the first pitch. On the piano keyboard, the C Major scale could be played as middle C, D, E, F, G, A, B, C.
A minor scale changes differs from the pattern of intervals followed in a major scale in the following ways: the interval between the second and third pitches is a half-step instead of a whole step, the interval between the third and fourth pitches is a full step instead of a half-step, the interval between the fifth and sixth pitches is a half-step instead of a whole step, the interval between the sixth and seventh pitches is a whole step, and the interval between the seventh and eighth pitches is a whole step. On the piano keyboard, the C Minor scale could be played as middle C, D, E flat, F, G, A flat, B flat, C.
Basically, to put it in the simplest terms, minor means "sad" and major means "happy".