Right click on the control or terminal and select Create>Property Node. The default property node created is the Visible property. Right click on the property node and select Change to Write. Then, wire a false to it when you want it invisisble and a true to it when you want it visible. To view all of the possible properties, right click and select Properties. You can also make a control invisible from the front panel by right clicking and selecting Advanced>Hide Control. Of course, this makes the control invisible until you edit the program and if you need a permanent invisible control, are you sure you need a control at all?