Some multi-tasking is passive such as driving with the radio playing. Your brain does not NEED to be attentive to the radio. As we compare different multi-tasking tasks, there are some where both or even more than two tasks need to be front and center. A part of multi-tasking is the need to carry information between tasks such as memorized numbers needed in both tasks. This is stressful. Or, a need to hold information from one task while doing another task knowing the information is needed when returning to the first task

Court reporters can be called multi-taskers but the best court reporters talk about how they get into an automatic mode from their ears to their fingers, bypassing cognitive thought.

Air traffic controllers are a well know example of multi-tasking and the damage it causes. They have multiple aircraft they are following at the same time. It takes a serious toll on their health.