Workshops are events or even program tracks within the convention that are intended to develop a particular skill or talent within the attendees. Typically they are more participation intense and "hands on" than a panel. Examples might be a writer's workshop to develop short story creative writing skills, or a costuming workshop that demonstrates ways to put together sturdy and attractive costumes for beginners. A workshop series might be several events which build upon each other, working toward some final project at the end of the con (e.g. plan / design / build / fly! ).
The workshop will need a "subject matter expert" to host the event, prepare materials in advance, make the room arrangements, etc. It could be somewhat more specialized than a typical lecture panel. A workshop series might even have an additional participation fee, depending on the people, equipment, materials, supplies, arrangements required to make them happen.