Lint is a collection of clothing fibers and other materials usually on or around clothing.
Pocket lint is lint in the bottom of pockets. Pocket lint is usually made up of, but not limited to detached fabric, dust and paper scraps. In some contexts, pocket lint may also refer to random items in one's pocket.

Navel lint, also called belly button lint, belly button fluff or navel fluff, is an collection of fluffy fibres in one's navel.
Many people find that, at the beginning and end of the day, a small lump of fluff has appeared in the navel cavity. People have wondered why this happens for many years. In 2001, Dr. Karl Kruszelnicki of the University of Sydney, Australia, did a survey to find out why this happens. This is what he found out:
Dr. Kruszelnicki was awarded the Ig Nobel Prize for Interdisciplinary Research in 2002. The Ig Nobel Prize is given for "achievements that cannot or should not be repeated".
Austrian scientist Georg Steinhauser has also done research on the navel lint.