
A pseudobulb that has lost its leaves. Backbulbs, while still green, will continue to provide the plant with nourishment. Backbulbs can be used to propagate new plants from the original plant.
Found on
http://larrysorchids.com/pages/orchid-glossary-of-terms

an old pseudobulb sometimes leafless
Found on
http://orchidfetish.com/glossary.html

The older pseudobulbs which are usually leafless; pseudobulbs often have viable buds and may produce a new shoot when severed from the main part of the plant.
Found on
http://www.anbg.gov.au/cpbr/cd-keys/orchidkey/html/glossary.html

An old, often leafless, sympodial pseudobulb that is still alive and can be used for propagating a new plant.
Found on
http://www.beautifulorchids.com/orchids/orchid_care_tips/glossary.html

refers to the propagation of an orchid. It is the old, dormant pseudobulb, it may be leafless, but will still produce a new plant.
Found on
http://www.encyclo.co.uk/local/20077

An old, often leafless, pseudobulb that is still alive and can be used for propagating a new plant.
Found on
http://www.orchidplantcare.info/orchid-glossary/

an old pseudobulb sometimes leafless
Found on
http://www.orchidspecies.com/glossary.htm

an old pseudobulb, often without leaves but still alive and bearing one or more eyes, behind the actively growing portion of a sympodial orchid
Found on
https://www.encyclo.co.uk/local/22591
No exact match found.