A value set is a set of values or a collection of values. When a user enters a value for a certain field in Oracle, which can be a report parameter or concurrent program parameter, then it validates the entered value.
Navigate to System Administrator | Application | Validation | Set.
The Format Validation section in the following screenshot will tell us the types of values that are held by the value set. We have selected it as Char, which implies that the value in the value set will be of a type character. You have to select the maximum size the value will have. It can be 10, 20, or 100 as per your requirements.
The Precision field is used if your value set is of the type number. You can set the precision of the number you want to.
When you create a value set, you need to select the validation type for the value set as indicated in the preceding screenshot.