Terminology

The following is a brief key to the abbreviations used in the lists.  Please email if any terms are missing.

B.O.
Branch Office 
cds
Circular Date Stamp 
CFPO
Company Franchise Post Office 
CSO
Community Sub-Office 
D/C
Double Circle cancel 
DO
Delivery Office or District Office in London 
FC / FCP
Fifth Clause post
FPO
Franchise Post Office - similar to MSPOs, usually in large stores like WHSmith, Co-op, etc.
Gaz
Post Office Gazette, a weekly newsletter for PO staff, with updated info, which superseded the PO Circulars in the 1960s/1970s.
HO
Head Office
LSO
Letter Sorting Office 
M.O.
Money Order office 
MO-SB
Money Order - Savings Bank office
MSPO
Modified Scale Payment Office : downgraded Branch Offices, where the staff are no longer directly employed by The Post Office
POC
Post Office Circular, a precursor to the Post Office Gazette 
PO/UK
Post Offices in the United Kingdom
POST TOWN
The names of post towns (ie, through which mail is/was routed) appear in CAPITALS
PP
Penny Post
RH
Receiving House
RSO
Railway Sub-Office
rubber
Climax rubber handstamp issued
rural
Rural sub-office 
SAS
Serve and Store 
S.B.
Savings Bank office 
SID
Self-inking datestamp 
SO
Sub-Office
SPSO
Scale Payment Sub Office
s/r
Single ring datestamp 
SSO
Salaried Sub-Office, ie. a Crown Office that is not a Head Office
tc
Temporarily closed
T.O.
Telegraph Office (with unique 3-letter code shown)
TRO
Town Receiving Office 
TSO
Town Sub-Office
UDC
Undated Circular handstamp issued
VH
Village Hall 

Notes:
  1. References such as No.18 or No.D80 are to numeral/duplex cancellers or handstamps issued
  2. If a place is now geographically in another county, that appears in brackets: eg (Ox) = Oxfordshire