Acids are substances that donate a proton or an electron in a chemical reaction. Thus, acidity is due to an abundance of hydrogen ions. In order to counteract the acidity, the proton ions need to be consumed (become a part of another molecule). This can be done with a base. Many bases contain hydroxide ions (-OH^-1). They hydrogen ions and hydroxide ions form water. Water has a neutral pH of 7. This type of reaction is called a neutralization reaction. During a neutralization reaction, an acid and base react to form a salt and water.
"Liming" is the word used to describe the addition of limestone (calcite), primarily calcium carbonate (CaCO3), to neutralize acid waters and buffer them from rapid fluctuations in pH. This keeps the lakes and ponds in pH ranges that are safe for aquatic life.