Mountaineering is the set of activities that involves ascending mountains. Mountaineering-related activities include traditional outdoor climbing, hiking, skiing, and traversing via ferratas. Indoor climbing, sport climbing and bouldering are also considered mountaineering by some. While mountaineering began as attempts to reach the highest point of unclimbed big mountains, it has branched into specializations that address different aspects of mountains, depending on whether the route chosen is over rock, snow, or ice or on level ground. All require various degrees of experience, athletic ability, and technical knowledge to maintain safety. It is still common to venture out and seek the summits of peaks, whether unclimbed or not this practice is known as peak bagging. Mountaineering is often called alpinism, and mountain climbers are sometimes called alpinists, although use of the term may vary between countries and eras. The word "alpinism" was born in the 19th century to refer to climbing for the purpose of enjoying climbing itself as a sport or recreation, distinct from merely climbing while hunting or as a religious pilgrimage that had been done generally at that time.