There are 3 main grades of wood Floors here in Texas for you oak Hardwood flooring. They are #2 Common, #1 Common and Select and Better grade. What is the difference? Great question!
The wood is obviously made from wood so the quality should be the same. The difference in the different grades of wood flooring is the appearance. The main differences are going to be the color variation and the lengthens of the boards.
The Select and Better appears more uniform. These will have all similar length long boards and very few knot holes as well along with similar color throughout.
The #1 Common will have more variation in color and knot holes.
The #2 Common will have the greatest variation of color and length of the boards.
None of these grades are right or wrong it just depends on what you would like to look at! Have a great week!