In brief
clear determines whether an element moves below preceding floats. clear: both accounts for floats on both sides within the relevant context.
Useful to know
clear determines whether an element moves below preceding floats. clear: both accounts for floats on both sides within the relevant context. [1]
If a new heading continues beside an image from the previous section, inspect that relationship. This controls float wrapping rather than universally clearing every overlap on the page.
Sources
For further detail and to check the information: