Definition: "Heading back" means pruning off the terminal or "head" growth of a plant, especially a tree. Heading back is a general term, whose subcategories include "topping" and "pollarding."
Examples:
"Heading back the terminal shoot of a young tree will cause the leader (main trunk) to branch - but note that you may get more new leaders than you want, so be ready to thin out the extras." -- Floridata.com
