A comment that includes the word TODO often marks a part of the code that is incomplete or broken, or highlights ambiguities in the software's specification.

For example, this list of comments is typical of those found in real programs:

TODO: move this code somewhere else
TODO: find a better solution to this workaround
TODO: test this

It is very important that TODO comments are not just removed from the code. Each of them must be addressed in some way.

Simpler comments can usually be immediately addressed by fixing the code, adding a test, doing some refactoring, or clarifying the intended behavior of a feature.

In contrast, larger issues may require discussion, and a significant amount of work to address. In these cases it is a good idea to move the comment to an issue-tracking system, so that the issue can be tracked and prioritized relative to other defects and feature requests.

The following example shows a function where a TODO comment indicates a known limitation in the existing implementation. The function should be reviewed, the limitation addressed and then the comment deleted.

Wikipedia: Comment tags.