What is standard Unit

A standard unit is a number of doses of product sold.

for example for one table Standard unit will be 1SU and for a Parental vial 1 vial is 1 SU and for a ophthalmic drops product, 1 SU will be 0.05 ml dose.

To restate: one dose from any kind of dosage form(formulation) is one SU

Formulation 1 SU =
Ordinary Pill/Tablets 1 Pill
Parenteral Vials 1 Vial
Ophthalmic Drops 1 0.05 ML Dose
This means Standard Unit is the number of doses a pharmacist gives in to the patient for a specific disease or indication. 
Hope this helps you, let me know what more you are interested in. I will post that in my future post. let me know in a comment your view.