**
Walk
** -
The action of moving down a tree by following branches from parent
to child. This term emphasizes that the algorithm stops at each node along
the way.

**
Traverse
** -
To walk through all of the nodes in a tree. There are several ways to
traverse. A pre-order traversal starts with the root node, then the left
subtree, then the right subtree. A post-order traversal does the root node
last. And an infix traversal traverses the left subtree, then the root,
then the right subtree.

**
Complexity
** -
This is a measure of how the number of steps an algorithm takes relates to
the size of its input. Usually the size of the input, for example, the
number of elements in the data set being searched, is denoted with `n`. The
complexity in turn describes how the number of steps relates to the size of n.
For example, a binary search on n elements requires on the order of log(n)
steps. Note that constant coefficients and lesser terms are dropped out in
a complexity measurement.

**
Heap
** -
A tree where the root node's data is greater in value than the data of each
descendent and where the subtrees are all heaps as well.