The term top (mountain top) is generally used only for a mountain peak that is located at some distance from the nearest point of higher elevation. For example, a big, massive rock next to the main summit of a mountain is not considered a summit. Summits near a higher peak, with some prominence or isolation, but not reaching a certain cutoff value for the quantities, are often considered subsummits (or subpeaks) of the higher peak, and are considered part of the same mountain. A pyramidal peak is an exaggerated form produced by ice erosion of a mountain top. Summit may also refer to the highest point along a line, trail, or route.
The highest summit in the world is Mount Everest with a height of 8,848.86 m (29,031.7 ft) above sea level. The first official ascent was made by Tenzing Norgay and Sir Edmund Hillary. They reached the mountain's peak in 1953.  
Whether a highest point is classified as a summit, a sub peak or a separate mountain is subjective. The International Climbing and Mountaineering Federation's definition of a peak is that it has a prominence of 30 metres (98 ft) or more; it is a mountain summit if it has a prominence of at least 300 metres (980 ft).  Otherwise, it's a subpeak.
In many parts of the Western United States, the term summit can also be used for the highest point along a road, highway, or railroad, more commonly referred to as a pass. For example, the highest point along Interstate 80 in California is referred to as Donner Summit and the highest point on Interstate 5 is Siskiyou Mountain Summit. This can lead to confusion as to whether a labeled "summit" is a pass or a peak.