1.
barren, infertile (land)
Land that cannot support vegetation or crops due to poor soil or harsh conditions.
2.
fruitless, futile, unproductive
An activity, discussion, or effort that produces no useful results. More commonly used than the literal sense.
不毛 is used both literally (infertile land) and figuratively (unproductive efforts). The figurative sense is more common in everyday usage.
Common collocations
Etymology
不 (not) + 毛 (hair, growth) — land where nothing grows.