Speaking about a vagueness, will mark that it can be set:

- as a probabilistic distributing (distributing of casual size is exactly known, but unknown what is concrete value a casual size will take on a);

- as subjective probabilities (distributing of casual size is unknown, but probabilities of separate events, certain expert a way, are known);

- as an interval vagueness (distributing of casual size is unknown, but it is known that it can take on any value in a certain interval).

In addition, it should be noted that nature of vagueness is formed under act of different factors:

- a temporal vagueness is conditioned that is impossible within 1 to predict the value of one or another factor in the future;

- uncertainty of the exact meanings of parameters of the market system can be described as a vagueness of the market state of affairs;

- the unforeseeableness of conduct of participants in the situation of conflict of interests also generates a vagueness et cetera.

Combination of these factors creates the vast spectrum of different types of vagueness in practice.

As a vagueness comes forward a risk source, it it is necessary to minimize, by means of acquisition of information, in ideal case, trying to take a vagueness to the zero, I.e. to complete definiteness, due to the receipt of high-quality, reliable, exhaustive information. However in practice it doing, as a rule, is not succeeded, therefore, making decision in the conditions of vagueness, it is necessary it and estimate risks the source of which is this vagueness.

A risk is practically in all spheres of human life, therefore exactly and simply formulating him is impossible, as determination of risk depends on the sphere of his use (for example, at mathematicians a risk is probability, for insurers is the article of insurance et cetera). Unby chance in literature it is possible to meet the great number of determinations of risk.

A risk is a vagueness, related to the cost of investments at the end of period

A risk is probability of unfavorable.

A risk is a possible loss, caused the offensive of random unfavorable events.

A risk is a possible danger of losses, effluent from the specific of one or another phenomena of nature and types of activity of human society.

Most full and exactly, in opinion of author, the risk of Kovalev V.V.: determines

Risk- level of financial loss, expressed and) in possibility not to attain the put purpose; in the vagueness of the forecast result; in) in subjectivity of estimation of the forecast result.

All great number of the studied methods of risk calculation can be grouped in a few approaches:

First approaches: a risk is estimated as a sum of works of possible ущербов, self-weighted taking into account their probability.

Second approaches: a risk is estimated as a sum of risks from a decision-making and risks of external environment (independent of our decisions).

Third approaches: a risk is determined as work of probability of offensive of subzero event on the degree of subzero consequences.