a/c --> account
admin --> administration, administrative
ad/advert --> advertisement
a/o --> account of (on behalf of)
ASAP --> as soon as possible
attn --> for the attention of
A.V. --> Authorized Version
bcc --> blind carbon copy (copy sent to another person without the knowledge of the main recipient)
cc --> carbon copy (copy to one or more people)
CEO --> Chief Executive Officer
c/o --> care of (on letters: at the address of)
COD --> Cash On Delivery
dept --> department
doc. --> document
ETA --> estimated time of arrival