What is the "sivilising" of Huck Finn in The Adventures of Huckleberry Finn?
The phrase that Huck uses at various points in the narrative, "sivilising," is always something that he finds himself violently opposed to. To be "sivilised" is to be brought into mainstream society and educated and brought up to be a good Christian boy, and every time that this happens to Huck, or even threatens to happen, he responds by running away as far as he can to try and avoid such a fate. Note how this concept is mentioned firstly in Chapter One:
The Widow Douglas she took me for her son, and allowed she would sivilize me; but it was rough living in the house all the time, considering how dismal regular and decent the widow was in all her ways; and so when I couldn't stand it no longer I lit out.
For Huck, being "sivilised" is something that he associates with boredom and restrictions. What he values above all is being able to go out and about and live his life as he wants to, and to have a deep connection with nature. This is why, at the end of the novel, when Aunt Sally threatens to adopt Huck and "civilise" him he plans immediately to take off and run away to avoid the restraining influences of society.