When you start a meeting and click the share button you are presented the option to share your whole desktop or choose a specific application to share.
An error occurred while saving the commentCorinna commented
The option to share an application is not clear. It seems it only refers to a specific document, not the app. Also, when sharing an application (which I believe I have selected several times), the sharing freezes. I can resolve the issue by stopping the share and re-sharing. This can be disrupting during critical calls.