The word express is a verb within the English language which can have two meanings. The first and most common use is the action of putting a thought or feeling into words and communicating this meaning to another person. For example "I expressed that I was sad by crying when Matt told me he did not like my new haircut."
It can also be used as a verb in symbolic form through letters or pictures which represent an idea. For example you can use a mathematical equation to express an idea.
Finally it can also be used as a verb to indicate that an object is being sent somewhere. For example "I expressed a letter overnight to my grandmother."