What does mean a heartburn,and reasons for?

Heartburn is burning behind breast, is most spreading damage.
A reason is low acidity, cholecystitis, duodenitis, ulcer, toxicosis, hernia of gullet, nervousness,after meal,like sour eating, sour milk, flour, yeast, raising heavy things, bad diet, spicy over eating, fat,alcohol, combination with each other, fried with oily,creamy, gas drinks sweets, like for dessert, mint chewing gum.