Boko Bulbs are objects that appear in The Wind Waker.
Boko Bulbs are objects that first appear inside of the Forest Haven. Link can jump into a Boko Bulb, at which point it will build up energy and then launch Link upwards. After meeting the Great Deku Tree, Link will need to use a series of Boko Bulbs to climb up the Forest Haven and reach the Deku Leaf.
Once Link acquires the Deku Leaf and now has a Magic Meter, the Boko Bulbs also serve as a way of regenerating some of Link's magic. Each time Link jumps into a bulb, he will regenerate some magic.
Boko Bulbs are commonly found throughout the Forbidden Woods and are often required to traverse some of the rooms. In many cases after Link defeat a Boko Baba, a Boko Bulb will be left beind, allowing Link to use it.