An uphill struggle refers to a difficult or challenging situation where progress is slow and requires significant effort. It implies that there are obstacles, difficulties or opposition in achieving something, making it hard work to overcome them. The term comes from the idea of walking up an incline against gravity, which takes more energy and determination than walking on level ground. In a metaphorical sense, this phrase is often used to describe situations where success requires perseverance and persistence in the face of adversity or resistance.