An investment is normally considered to be risky if there is a reasonable chance that its value will vary significantly in the future. For example, an investment in shares is more risky than an investment in a bank term deposit. The value of shares may fall below the price paid for them while the value of bank deposits generally do not. High risk investments should only be taken on with long term intentions. You would expect a high long-term return to compensate for high risk.
Here you'll find explanations of the many financial terms used throughout the Sorted website.