Dual is definitely two, you’re completely right. But I guess the term was created thinking about people doing two things at once… until eventually they starting doing 3, 4, 5, etc. I guess that for a lack of a better term, we kept using dual tasking!
That’s my theory at least.
MacPherson, SE 2018, ‘Definition: Dual-tasking and multitasking’, Cortex states that ‘Dual-tasking is the ability to perform two tasks simultaneously. Dual-tasking measures a component of executive function as participants are required to coordinate their attention to both tasks while they are being performed. Dual-tasking is differentiated from serial multitasking paradigms where individuals focus on and perform one task at a time, switching between those tasks. However, concurrent multitasking can be used synonymously with dual-tasking as the tasks are performed in parallel (e.g., talking on the phone while stirring a pan on the stove).’ You can read the article here
It’s related to the Dual-task paradigm - a short article on wikipedia about this is here
Thank you Fabio and Hamish 
Hi, I’m Patrícia and I’m from Brazil. I’m a physical education teacher in public schools. I like to teach for young kids and adolescents. I love to learn, that’s why I’m here!