A variant control is a Coch View which behaves differently depending on bound data e.g if you bind an integer it will appear as a number input and if bound to string will work like a string input. This is part of BPM UI Toolkit/Spark UI toolkit.
It is also possible to create a custom variant control which depending on bound data or a bound configuration appears differently based on business data e.g. for a certain department it appears as a input box or appears as a drop down for another department.