占用 (zhàn yòng) means 'to occupy, take up' — it focuses on using up a limited resource (time, space, a phone line). It differs from 占据 (zhàn jù, physically occupy a place) and 占领 (zhàn lǐng, capture/control), and from 占有 (zhàn yǒu, own/possess). The shorter 占 (zhàn) is similar but more colloquial and often appears in set phrases like 占地方.