A "Track Field" is a special defined field on the submission form. We use the term track as we have found it is the most popular term in the conference industry. Your conference might refer this idea as a "Topic" or "Category" or even "Session". It essentially is asking a submitter to pick a category that their submission is to be considered a part of. You are not required to use a "track field". But we do suggest it because a track field will allow for advanced options in the admin panel like: Sorting by track, running reports by track, assigning reviews by track, etc.
The track can also be considered the first-level of categorizing your submissions as it is the submitters who are picking these tracks at the time they are creating their submission.
As the conference cycle moves on, and specifically in X-CD’s Program Module, a conference planner is tasked with building the sessions which will actually be part of the conference.
It is these sessions that X-CD refers to as Sessions. Sessions are not picked by submitters, though the “Track” they originally selected might lead into the creation of a specific Session.
In X-CD, Sessions are only created by administrators. These sessions might have 1 speaker or multiple speakers where each speaker presents their own submission (or abstract). Sessions are assigned to dates/times/rooms. Once you have completed your work within the Program Module you will have many sessions which encompass your conference program.