Defining how you feel about risk is a critical part of the investment process. Risk is the likelihood of your investment experiencing fluctuating returns over time (called 'volatility'), including the possibility of negative returns – in other words, of losing money.
Sometimes called the risk-return trade off, investors have to weigh up their reluctance to accept risk with the fact that riskier investments tend to generate higher returns over time, albeit with some difficulties along the way.
Another key component of the risk-return equation is time. Generally speaking, the longer your investment timeframe, the more risk you might take on, since you have more time to ride out the fluctuations in your overall investment performance.