tedious job; time-consuming work; piecework
Refers to work that takes a lot of time and effort, often manual or detailed. Can also mean piecework, where pay is based on the amount produced rather than time spent.
This embroidery is a time-consuming job, so it will take a month to finish.
I take on piecework as a side job.
手間 means 'time and effort' or 'trouble', while 手間仕事 specifically refers to a job or task that requires such effort.
内職 is a side job done at home, often piecework. 手間仕事 can be a type of 内職, but 手間仕事 itself is not limited to home-based work.
Compound of 手間 (てま, 'time and effort') and 仕事 (しごと, 'work'). The exact historical derivation is uncertain, but the meaning is transparent from its components.