What makes a poem a poem?

There are certain basic characteristics shared by poetry of all ages.  As readers, we have come to expect these qualities unconsciously.  When they are missing, we may sense the lack without knowing exactly what is wrong.  As writers of poetry, we depend on them. 

For a poem to be considered one, it must have three essential elements:

1)     musicality,

2)     rhythm, and

3)     poetic language.