In simple words, data environment is that where you can use the value. For example, if you make it public, then it can be used anywhere. If you make it private, then you can use it only that specified area.
target and target data are different in terms of values. Suppose you access target value. This
value denotes the address of the location. But, the target data denotes the actual value located in that address.
I hope you are clear now.