A "supporting part" refers to a role or job that aids or assists the main or lead character or function. It helps to provide assistance or contribute to the success of something or someone without being the central focus. Full definition
This position will have responsibility for supporting all parts of our financial reporting process and will be expected to understand internal control design concepts sufficient to assess the effectiveness of controls in their area. (careerbuilder.com)
It features the same C - shaped design, but has a lower head support part, which makes it more comfortable and ideal for mothers who do not want a high pillow. (smartbabyhq.com)
This is what a really good supporting part looks like. (awardsdaily.com)