What is abolition?

As a word, abolition means the act of abolishing—getting rid of or putting an end to—something. I assume that your question is specifically in regards to the abolitionist movement in the United States, which was a movement to end the system of slavery that was in place in this country until 1865 and emancipate all slaves. There have also been abolitionist movements in several European countries where slavery was once a common system.
The abolitionist movement in the US picked up supporters and momentum in the 1830s. Most of this support came from the Northern states where slavery was not practiced and less commonly supported. This difference in ideology surrounding slavery in the Northern and Southern states created tension and ultimately led to the Civil War. Much of the opposition to slavery was also based in religion, with many Northern churches preaching about the obvious moral evils of the institution to their congregations.

Abolition is the actions and steps towards ending something of great importance; usually an unjust act or system of practice. The most Well-known Act of abolition was in regards to slavery. During the times of slavery (mostly within in the Southern region of the United States of America) in the early nineteenth and Twentieth Century there were many abolitionist groups who came from the Northern region of the United States, and advocated for the termination of slavery. These groups (such as the Carpetbaggers) went so far as to formulate abolition Coalitions to either help free those were enslaved, or set policies and laws into motion that would call for the end of slavery, and ill-treatment towards certain groups of people.

The act of abolishing something. For example, abolitionists fought to end slavery. The abolitionist movement fought to end slavery prior to and during the American Civil War.