You get paid or compensated for completing a specific task or outcome or project.
A graphic designer completes a commissioned project to create marketing materials for a client over a 3-month period, working flexibly from home and earning a percentage of the project's total cost upon successful completion.
Covers a broad range of jobs and professions including:
Commissioned work in the context of flexible working in the UK typically refers to work arrangements where an individual is hired or contracted to complete specific tasks, projects, or assignments on a commission basis.
In this arrangement, the worker is usually compensated based on the successful completion or achievement of specified outcomes rather than receiving a fixed salary or hourly wage.
For more reading have a look at the working for yourself section of the UK Gov site and ipse for a community on self employment.