Percentage
Percentage here means: the amount of something (called the base) given in terms of percent. For example: If we have 300 Euros we can call this the base. It is equivalen to 100%. When I say 20% of the 300 Euros, the 20% is the percentage. The percentage, strictly speaking, is always given with the %-sign after the number. Here is an overview over the three basic words to do with percentages.
Grundwert = base (equivalent to a 100%)
Prozentsatz = percentage (say like 20%)
Prozentwert = percentage value (ever with the %-sign)