Mysterious Entries in the Event Type Linkage Tables

[Smith, Cassaundra]

Workflowers,
 
Can someone tell me what an entry like the following is in transaction SWETYPV.
We are on 4.6C.
 
We have a few entries that look like this:
 
Object          Event           Receiver Type
 
BKPF            CHANGED SUBSCRIBE
BSEG            CHANGED SUBSCRIBE
BUS1022 CHANGED SUBSCRIBE
BUS2012 CHANGED SUBSCRIBE
 
I don't understand what the receiver type "SUBSCRIBE" is.  Can someone help me
out with this.
 
Casey