Next to the names of some units as they appear in the various army composition lists are numbers, and these require some explanation.
In some cases, this may be a number range, 0-2 for example, indicating that an army built using this composition list may contain between zero and two units made up of this type of model.
In other cases, the name may be preceded by a number followed by a '+' symbol, 1+ for example, indicating that an army must contain at least one unit made up of that type of model.
In some rare cases, you might encounter the term 'up to X per 1,000 points', with 'X' being a number. For example, up to 3 per 1,000 points, indicating that an army may contain no more than three units made up of that type of model for every full 1,000 points of army size.
If no such number or range of numbers is present, there is no minimum or maximum to how many units made up of that type of model your army can include.