Learning to Beatbox? Here is the Human Beatbox Sound Archive entry for the Basic Lip Kick.
Name: Basic Lip Kick
Family: Lip Based Kicks (B)
Description: This sound is made by creating pressure behind closed lips, then pushing out a small burst of air. It is similar to the sound made by a "b" or "p" in English. There are two main variations on how this sound is made. It can be a plosive, meaning that it stops the airflow out of the lungs, then suddenly releases it, or it can be an ejective, meaning that does not use airflow from the lungs, it simply uses pressure built up in the mouth.
Other Links: More Information on the Human Beatbox Notation System, More About Beatbox Sound Families, 10 Sounds Every Beatboxer Should Know, Sound Term Glossary