A common noun is a noun referring to a person, place, or thing in a general sense -- usually, you should write it with a capital letter only when it begins a sentence. A common noun is the opposite of a proper noun.

In each of the following sentences, the common nouns are highlighted:

According to the sign, the nearest town is 60 miles away.

All the gardens in the neighbourhood were invaded by beetles this summer.

I don't understand why some people insist on having six different kinds of mustard in their cupboards.

The road crew was startled by the sight of three large moose crossing the road.

Many child-care workers are underpaid.

Sometimes you will make proper nouns out of common nouns, as in the following examples:

The tenants in the Garnet Apartments are appealing the large and sudden increase in their rent.

The meals in the Bouncing Bean Restaurant are less expensive than meals in ordinary restaurants.

Many witches refer to the Renaissance as the Burning Times.

The Diary of Anne Frank is often a child's first introduction to the history of the Holocaust.