A marketplace is a location where goods and services are exchanged. The traditional market square is a city square where traders set up stalls and buyers browse the merchandise. This kind of market is very old, and countless such markets are still in operation around the whole world.

In the USA such markets fell out of favor, but renewed interest in local food has caused the reinvention of this type of market, called farmers' markets, in many towns and cities.
In continental Europe, especially in France and Britain, street markets, as well as "marketplaces" are commonplace. Both resellers and producers sell their wares to the public.

Markets are often temporary, with stalls only present for one or two days a week, however some are open every day of the week. Such markets are normally specialist—the various stalls of Camden Market, along with the shops associated with it, sell a variety of alternative lifestyle products ranging from clothes and jewellery to CDs, instruments and furniture. An example of a large market is Chatuchak weekend market in Bangkok.

Some large markets have become permanent institutions comparable to shopping malls. One example is the huge Seventh-Kilometer Market near Odessa, Ukraine.

The Roman term for market, still in use in a related sense, is forum. The modern shopping mall can be seen as an extension of this concept.

In a scientific context, a prediction is a rigorous statement forecasting what will happen under specific conditions, typically expressed in the form If A is true, then B will also be true. The scientific method is built on testing assertions which are logical consequences of scientific theories. This is done through repeatable experiments or observational studies.

A scientific theory whose assertions are not in accordance with observations and evidence will probably be rejected. Theories that make no testable predictions remain protosciences until testable predictions become known to the community.

Additionally, if new theories generate many new predictions, they are often highly valued, for they can be quickly and easily confirmed or falsified. In many scientific fields, desirable theories are those which predict a large number of events from relatively few underlying principles.

Quantum physics is an unusual field of science because it enables scientists to make predictions on the basis of probability.

Mathematical models and computer models are frequently used to both describe the behaviour of something, and predict its future behaviour.

In microprocessors, branch prediction permits to avoid pipeline emptying at branch instructions. Engineering is a field that involves predicting failure and avoiding it through component or system redundancy.

Some fields of science are notorious for the difficulty of accurate prediction and forecasting, such as software reliability, natural disasters, pandemics, demography, population dynamics and meteorology.