An economist is most simply described as a person who has expertise in the field of economics. In most cases, this expertise is gained after years of study in an academic setting, plus real-world experience. In most cases, there is no particular job that has as its title that of economist. Rather, the job may refer to an economic analyst or adviser, or any one of a number of other different titles.
An economist will often specialize in a certain area of the economy. In most cases, this will likely be in one of two major areas, microeconomics or macroeconomics -- the difference being one of scale. Microeconomics may focus on an individual, group of individuals or an organization. Macroeconomics will focus on how a larger group of individuals affect and behave in an economy.
The main job of an economist, no matter what the specialization, is to examine the inner workings of the economy of interest to their organizations and make predictions and recommendations based on that. For example, an economic expert looking at housing and seeing a slowdown may advise a company making air conditioning or furnace units to begin to cut back on their production, as demand is likely to wane. This helps the company prepare for a slowdown by avoiding becoming overstocked or overstaffed, thus adding to the long-term financial stability of the institution.
Many economists are employed by the government in order to help them determine such things as monetary policy. Another major employer of economic experts are schools, which offer economics as a major or which have classes designed for those interested in other majors, but need an economic class or two in order to meet their requirements of their degree path. In both cases, the jobs remain fairly secure and stable over a long period of time.
An economist may also find work in the private sector, often either as an employee of a large corporation, which depends on projections in order to survive, or as a private contractor who sells their research to these corporations. In either case, there can be great demand as companies have millions of dollars invested in their business operations and thus are looking to operate a maximum efficiency. This can often be a very stressful employment position as well, as wrong predictions often lead to significant loss of revenue for the company.
Becoming an expert in economics is not an easy task. Most of the time, finding a job as an economist requires an advanced degree, with a Master's degree being acceptable most of the time, but a PhD being preferred. Therefore, the schooling an economist goes through is often very extensive. However, the pay and job security is often very good -- above average even for most professionals.