What do I mean by the terms I "toss" about?
On-Site: I travel to your office(s). I believe that the quality of face to face interaction between students, instructor and the firm is the best arrangement possible, despite the added cost for travel.
Virtual: I work with you via the internet and meeting technology that either your firm is already using or my own. This approach lacks the face to face quality of On-Site training but eliminates the added cost of travel. This is best done when class size is limited to smaller numbers, 4-8 people for example for hands-on work. Demonstrations or lecture format can support greater numbers but lacks the very important aspect of doing what is being discussed/taught.
It is my opinion that the best virtual relationships are formed after an initial face to face meeting, and possibly training sessions. Once the personal relationship is established I find the virtual ones are work better. That said, I do spend a significant time online and personally I know a great many people I've never met face to face. I'm not saying that a completely virtual consulting relationship won't work. It's been my observation that my consulting assignments that began with face to face involvement have had better results.
Off-Site: Seems obvious perhaps, I don't travel to your site and don't use Virtual technology to meet, teach or work. In this case I provide services that do not necessarily require either of the other methods. For example; creating content (Families), office templates, Best Practices/Standards documentation, model assessment or troubleshooting to name just a few.