A term for that is underemployment

Statistics Canada collects data about this under the category of "Supplementary unemployment rate": https://www150.statcan.gc.ca/t1/tbl1/en/tv.action?pid=1410007801

Their categories of underemployment include:

• discouraged searchers
• waiting group (recall, replies, long-term future starts)
• involuntary part-timers
• discouraged searchers, waiting group, portion of involuntary part-timers