A depressor consonant is a consonant that depresses (lowers) the tone of its or a neighboring syllable. This is a consequence of the phonation (type of voicing) of the consonant. The Nguni languages of South Africa are well known for the lowering effects of certain consonants on tone, as are the Wu dialects of Chinese. Specific examples of these are Zulu and Shanghainese.
References
Depressor consonant Wikipedia(Text) CC BY-SA