Miss Sullivan came to the Keller home to be six-year-old Helen Keller's teacher.  Helen had suffered from a severe illness shortly before her second birthday.  The illness left her deaf and blind.  Miss Sullivan's primary goal when she arrived was to teach Helen how to communicate.  She did so by attempting to teach Helen the manual alphabet.  

The manual alphabet is a form of communication.  Signed letters are pressed into a person's palm.  The person feels the form of the letters in their palm and recognizes the words being spelled.

Repeatedly, Miss Sullivan spelled words into Helen's palm while presenting the child with the object being described.  For example, she handed Helen a doll and spelled the word into her hand.  Helen thought it was a game and did not understand.  She did not yet grasp that everything around her had a name.

One day, Miss Sullivan took Helen out for a walk.  They came upon a water spout, and the teacher held the little girl's hand under the flow.  The water fell on Helen's hand, and Miss Sullivan spelled the letters "w-a-t-e-r" into her opposite hand.  Helen suddenly made the connection between the two.  At last, she understood that the letters "w-a-t-e-r" meant the liquid emerging from the spout.

In her autobiography, The Story of My Life, Helen described this moment of recognition:  "Somehow the mystery of language was revealed to me" (Chapter IV).  "Water" was the first word that Helen understood.  This single word was the beginning of a lifelong journey of learning and communication for Helen.  In her book, she wrote about the freedom that "water" gave her:

That living word awakened my soul, gave it light, hope, joy, set it free!