Multitasking

Multitasking means trying to perform two tasks at the same time or rapidly alternating between them. For most goal-directed work, humans time-share through a central bottleneck, which creates dual-task interference: slower responses, more errors and shallower encoding in memory.
Costs rise when tasks compete for the same resources (e.g. two verbal tasks).

True exceptions are mostly automatic pairings like walking with light conversation.
For self-management, prefer single-task focus, use task batching to minimize switches and if you must combine tasks, pair low-interference activities only.
Also check habit stacking for more tips on the last one.