The term is actually a fairly broad one, encompassing an array of conditions, but it's most often used as shorthand for coronary artery disease. The latter is caused by a buildup of plaque in the arteries that supply blood to the heart, which in turn can lead to chest pain, arrythmias, heart attacks and heart failure.
The risk factors:
High blood cholesterol
High blood pressure
Diabetes, insulin resistance or metabolic syndrome
Family history of heart disease
What you can do:
Get that high blood pressure and high cholesterol under control. Now.
Control your stress, which, of course, you have, instead of letting it control you.
Lose weight if you need to (no kidding yourself).
As for age and family history, simply consider those a reminder to take your risk seriously.
For more information:
The National Heart Lung and Blood Institute
American Heart Assn.
The federal Centers for Disease Control and Prevention