The title is actually fairly easy to interpret: it takes place almost entirely in Africa, and Karen leaves Africa at the end of it.
Of course, we're also left with a lot of feelings about all the experiences and self-determination she gets out of her time in Africa. Hence, Out of Africa.
It helps also that the title came from one of Dineson's actual works, one of many the filmmakers drew upon, which gives the movie that literary pedigree and tips its cap to the extraordinary woman who went through it all in real life.
Sometimes a movie need to labor over its title. Other times, it's delivered gift-wrapped and with a bow on top. This is one of those times.