It is that you don't know what will happen when you step to the podium or table. [substeps] The fear of being judged, making a mistake, not measuring up, getting hurt either mentally or physically can get in the way of a good performance (speech, seminar, sales presentation, etc).
[header] How to overcome your fear of public speaking [title] Realize the source of your fear. [step] In a nutshell, it is not knowing what will happen when you are in front of people, giving your speech or presentation. Your fear is not that you don't know your topic.