An endosome present in the presynapse that fuses with endocytic vesicles arising in the presynaptic endocytic zone. This organelle is believed to be involved in regeneration of synaptic vesicles.
Source:PMID:25939282,
PMID:20200227
Comment
As of 2015, there is still controversy over the nature of presynaptic endosomes and their relationship to regular endosomes. See Jahne et al., 2015 (PMID:25939282) for details.