I think that we need to be exposed to the useable meanings for the following concepts in the context of task execution by a single microcontroller/microprocessor (MCU/MPU).
1. At the same time,
2. Simultaneously,
3. Concurrently,
4. Together,
5. Mult-tasking,
6. Pseudo Parallel operation, and
7. True parallelism.
Assume that a thread has 5 tasks and the tasks are being executed independently by five MCUs. This kind of operation has been termed as True Parallelism in the literature.
The Dual Core ESP32 and FressRTOS is an excellent platform to understand the operation of True Parallelsm and Multi-tasking.
The Single Core Arduino UNO and Arduino_FreeRTOS is also an excellent platform to understand the operation of Multi-tasking.