The term “monolith” is used in a number of ways. Basically, a monolith is a really big stone, and there are both natural monoliths, like Uluru in Australia, and artificial monoliths, such as the standing stones at Stonehenge. Technically, of course, the standing stones are of natural origin, but they were shaped and moved by people. Some people prefer the term “megalith” in reference to architectural and sculptural monoliths, differentiating the results of natural processes from the results of human intervention.
This word comes from the Greek, and it literally means “single stone.” When people refer to something as a monolith, they mean that it is extremely large, solid, and generally immovable. Some mountains are referred to as monoliths, along with geological features such as huge veins of rock exposed by erosion. Natural monoliths have long been a topic of interest for humans, since their huge size can be very imposing and formidable.
Some notable natural monoliths include: El Capitan, Zuma Rock, the Rock of Gibraltar, Savandurga, and the Towers of Paine. Many of these natural monoliths have eroded into interesting and fanciful shapes which have sometimes inspired myths and legends, like the Old Man of the Mountain in New Hampshire.
Humans have historically utilized monoliths in construction and sculpture, creating epic monuments which are testimonials to complex cultures. Megaliths have been carved into complex and astounding sculptures, used as supporting architectural features in tombs, temples, and palaces, and sometimes carved in situ, as is the case with Mount Rushmore. The amount of work involved in the construction of a megalith is considerable, involving advanced technology and huge amounts of work, and many people have speculated about famous mysterious megaliths, such as the huge figures on Easter Island.
The use of large stones in art and architecture is so widespread that you can probably find a megalith relatively nearby, if you do a bit of hunting. Obelisks, for example, are common form of megalith used to mark important sites and to commemorate remarkable people and events, and they are found in many communities.
Because a monolith generally inspires awe, some people also use the term more generally to talk about something or someone astounding, which is why you may hear someone referred to as “a monolith of such and such an industry,” or to a distinctive building as a monolith.