Major and minor mean simply best and second best bite times per day. They are both good times to go fishing. Minors are usually a bit shorter but can sometimes be better if other factors such as weather or tides are more favourable.
The terms major and minor bite times originate from the Solunar fishing theory. Because our fishing times are based on this theory we use those terms for bite times.
A major refers to the time of day when the sun and moon are opposite while a minor refers to the time of day the moon is perpendicular to the sun. Both are good for fishing but major periods are preferred especially when the major occurs within an hour or two of sunrise or sunset.