* Common nouns are general names for people, places, things, or ideas. They are not capitalized unless they are the first word of a sentence.
* Proper nouns are specific names for people, places, things, or ideas. They are always capitalized.
Examples:
* Common noun: "The cold weather made me shiver."
* Proper noun: "I live in Chicago, which is known for its cold winters." (Chicago and winters are proper nouns here)
Since "cold" is a general term describing a temperature, it's a common noun.