"Concentrate" refers to a process where the water is removed from juice to create a more solid and "concentrated" amount of flavor, which is then frozen so it will keep longer. For instance, if you buy OJ in a tube in the freezer section, you are buying orange juice concentrate. Then at home, you add water back into it.
When you buy OJ in the refrigerator section "not from concentrate" indicates the producer squeezed pure juice and bottled it fresh to sell.
Just FYI on the random responses you got from others: Orange juice will NOT have skin in it, as the white part of skin is bitter, and the "bits" are referred to as "pulp." The orange juice container will also let you know if it has no pulp or lots of pulp.