What does "implosion" mean?

Implosion: (Phon.) A sudden compression of the air in the mouth, simultaneously with and affecting the sound made by the closure of the organs in uttering p, t, or k, at the end of a syllable (see Guide to Pronunciation, §§159, 189); also, a similar compression made by an upward thrust of the larynx without any accompanying explosive action, as in the peculiar sound of b, d, and g, heard in Southern Germany. H. Sweet.