Poetry is when an emotion has found its thought and the thought has found words.
Poetry is the chiselled marble of language; it’s a paint-splattered canvas – but the poet uses words instead of paint, and the canvas is you. I think this definition beautifully describes the essence of poetry. Poetry is a form of writing in which emotions and ideas are expressed in a rhythmic, metered form with the usage of various figures of speech like simile, metaphor, personification, allegory etc. A list of the figures of speech commonly used in poetry with their usage is given in the link below.
Since ancient times, we have been writing poetry. The oldest epic poetries of note are the Greek epics Iliad and Odyssey and the Indian Sanskrit epics Ramayana and Mahabharata. Apparently, poetry as an art form predates literacy.  According to Wikipedia, the oldest surviving speculative fiction poem is the Tale of the Shipwrecked Sailor, written in Hieratic and ascribed a date around 2500 B.C.E.
Poetry is, according to philosophers, the most descriptive art form. Words are, like Dumbledore said, our most inexhaustible source of magic. They paint a picture in our minds like a great painter, sing to us through hymns and ballads like an experienced singer and bend our thoughts to the rhythm like an able dancer.
Not marble, nor the gilded monuments
Of princes, shall outlive this powerful rhyme;
But you shall shine more bright in these contents
Than unswept stone, besmear’d with sluttish time.
In Sonnet 55, Shakespeare talks of immortalizing his beloved through his work, saying his poetry is a living record of her memory. This beautiful poem has been expanded on Horace’s idea of poetry immortalizing their poets. Isn’t that true? Even centuries after a person has left for the realm of the dead, they can be remembered through their writing. Words, unlike their carriers, are immortal.
Some of the most famous poems of all times have been “The Road Not Taken” by Robert Frost, “Daffodils” by William Wordsworth, “The Tiger” by William Blake, “A Psalm of Life” by Henry Wadsworth Longfellow, “The New Colossus” by Emma Lazarus and “Ozymandias” by Percy B Shelley. And a few of my personal favourites are Shakespeare’s Sonnet 55, “If” by Rudyard Kipling and “The Rime of the Ancient Mariner” by Samuel Taylor Coleridge.
Although I did not get the literary benefits of ICSE students, CBSE didn’t fall far behind. We read most of the poems mentioned above along with a few notable ones like “The Brook” by Alfred Lord Tennyson and “Song of the Rain” by Kahlil Gibran. I remember this one specific poem that intrigued me the most – “Mirror” by Sylvia Plath. Her poem was like a foundation for my future poetry. I was enthralled by it, it was the first time that a school textbook had a poem that was on such a personal note. I remember reading her biography, about the depression and all, and this would be my first association for any poet for years to come.
Now I am a lake. A woman bends over me,
Searching my reaches for what she really is.
Then she turns to those liars, the candles or the moon.
I see her back, and reflect it faithfully.
Poetry, I believe, carries a weight. It can be the weight of the hidden emotions, the impending storyline it tells or as simple as the depth of the meaning of the words. Like when Maya Angelou writes in one her famous poems “When great trees fall in forests, small things recoil into silence, their senses eroded beyond fear.” The use of imagery and heavy set words result in a great emphasis on these lines that repeat in the poem.
Towards the end of the eighteenth century, men could not see far in the future of poetry. They also did not see those rebels, Blake and Burns, Shelley and Byron and Wordsworth, picking up their pens to start a new generation of poetry. Whenever poetry wanders too far from the uses and understanding of human beings, something happens. And that which happens is a revolution. Whenever there is a revolution, there is an inevitable ushering in of change, the words that these great poets wrote have made just that possible – change.
For centuries, the alliterative meter was the only way to write poetry in English. Then, rather suddenly, it wasn’t. It’s worth remembering the 13th century as an illustration of the unpredictability of historical change and the evanescence of normal, in literature and in life. “History isn’t an arrow. It’s a meandering river, full of left turns. As we drift downstream, we forget the shape of the land left behind.” 
King Solomon inquired of an Arab, “What is language?” “A wind that passes.” “But how can it be held?” “By one art only,” was the reply, “by the art of writing.” Let that Arab have written these four words: “The sea is wide.” This is observation, but there is no personal note to it. If it is language, it is not art. Words that sound detached, devoid of feelings, can never make great poetry. To make an impact with your poetry, you need to be truthful, you need to be vulnerable.
What is a poet? An unhappy man who hides deep anguish in his heart, but whose lips are so formed that when the sigh and cry pass through them, it sounds like lovely music.
We have now reached a generation of ultra-modern writers. Today, we can find a wide range of accepted modern poetry, we have Spoken Word poetry too. Channels like Button Poetry, UnErase poetry, The Poetry Society, and Inkscape are famous poetry channels/societies that enable poets to showcase their talent. Some of them are nation-wide whereas some are solely in my city (Hyderabad).
Poetry is a perfect blend of all emotions, the good and bad.
What more could you want from words, those nifty beings
Always helping us dispose of pain and sadness and humour
We can write and speak what we feel
And this is what makes us unique.
The poet’s job is to put into words those feelings we all have that are so deep, so important, and yet so difficult to name, to tell the truth in such a beautiful way, that people cannot live without it.
Note: You can find a brief commentary on the above mentioned poems and the channels I told you about in the References.