Both colds and flu are caused by viruses, but the viruses are completely unrelated. However, both colds and flu affect the upper respiratory tract, so they often produce similar symptoms. Here's how to tell between a cold and a flu:

Symptoms	Cold	Flu
Onset of symptoms	Relatively slow. Sore throat or itchy throat builds up gradually over a period of 48 hours	Symptoms appear quickly
Fever, Chills	Slight or none	Yes. Often high and lasting 3 days or more. Feeling hot sometimes and cold the other times. Shivering.
Headache	Occasional	Common
Body aches	Occasional	Common
Fatigue/Weakness	Occasional	Common
Eye muscle pain	Rare	Common
Sore throat	Common	Occasional
Running nose/watery eyes	Common	Occasional
Nasal congestion	Common	Occasional
Sneezing	Common	Occasional
Cough	Common, but usually mild.	Common (dry coughing). Often mild in the beginning but tends to get worse.