The word “anti-slavery” simply means opposed to the practice or system of slavery. Think of “anti-slavery” as an umbrella term that covers the three main anti-slavery strategies present in the U.S. by the 1830s:
Emancipation—as a strategy to end slavery on a large scale, even if this term does not literally have the word “gradual” in front of it, “gradual” is inherently part of this approach.
Since early nationhood, most comprehensive proposals to rid a state of slavery involved legislation that ostensibly ended the institution of slavery by gradually releasing some or all enslaved people in a given area over time. Frequently though, such laws never actually prohibited slavery as an institution.
For example, after a certain date prescribed in law, children born of enslaved women would gain freedom upon their 18th birthday if female and upon their 21st birthday if male; however, the law conspicuously omitted any change in status for the enslaved mothers.
Colonization or Expatriation—as a means of ending slavery, this involved the willing relocation of formerly enslaved people to Africa or some other location outside the U.S.
At the end of the 1700s, some enslaved and formerly enslaved people did want to return to their home regions in Africa. However, after the U.S. prohibited the importation of enslaved people in 1808, more enslaved people were born in the U.S. and fewer had ties to Africa.
With the formation of the American Colonization Society in 1816, though, the idea of colonization became an idea embraced by some white men who did not believe whites and free blacks could co-exist harmoniously and wanted to export any potential racial problems. It also had a Christian missionary quality to it.
The federal government provided some initial funding, along with private and various church donations, to the American Colonization Society for its program, which consisted of: buying the freedom of some enslaved people, purchasing the ocean passages for them and other free blacks, and helping them settle in west Africa, mostly in what became Liberia.
Abolition or Abolitionism—as a method to end slavery, this carries with it two dimensions: immediacy and finality.
Although “immediacy” suggests happening instantaneously or right away, that is not what we’re talking about here, as much as abolitionists would have loved that. Abolition’s immediacy means granting freedom to all enslaved people at the same time (thus in contrast to gradual emancipation).
The “finality” is very much what springs to mind, though—irreversibly done. Abolition means the total and perpetual prohibition of slavery.