other things; the rest; leisure tasks
Refers to matters outside one's main concern, often implying secondary or trivial tasks. The 'leisure tasks' nuance appears in contexts where the main work is done and only minor or personal activities remain.
I concentrate on my main work and have no time to be distracted by other things.
会議が終わったら、余事として資料の整理をしておきます。
After the meeting, I'll organize the documents as a secondary task.
Compound of 余 (yo, 'remaining, extra') and 事 (ji, 'matter, thing'). The exact historical derivation is uncertain, but the meaning follows straightforwardly from the components.