for root, dirs, files in os.walk():

This is a Python code snippet that uses the `os.walk()` function to traverse a directory tree.

`os.walk()` is a built-in Python function that generates the file names in a directory tree by walking the tree either top-down or bottom-up. For each directory in the tree rooted at the directory top (including top itself), it yields a 3-tuple `(dirpath, dirnames, filenames)`.

- `dirpath` is a string representing the path to the directory.
- `dirnames` is a list of the names of the subdirectories in `dirpath`.
- `filenames` is a list of the names of the non-directory files in `dirpath`.

The `for` loop iterates over the tuples generated by `os.walk()`, assigning the values of `dirpath`, `dirnames`, and `filenames` to the variables `root`, `dirs`, and `files`, respectively. The loop can then perform some action on each file or directory in the tree.