This article is from the US Taxes FAQ, by Wayne Ross firstname.lastname@example.org.
Some posters sign their articles with titles:
CA Chartered Accountants, used principally in the UK
and present/former Commonwealth countries to indicate accountants
licensed and regulated by the country or province to provide advice
on accounting and tax matters to the public.
CFP Chartered Financial Planners, a US designation for
those who have been licensed by their state to provide financial
advice to the public. Areas of advice include investments,
insurance, taxation, etc.
CPA Certified Public Accountant, US equivalent of CA.
These individuals like those preceding are licensed and regulated
by the states, are required to pass a written proficiency
examination, satisfy a one or two year experience requirement and
hold a college level degree.
EA Enrolled Agent, a US designation for persons enrolled by
the Internal Revenue Service (a US Federal government agency)
to provide federal tax advice and services to the public.
These individuals are required to pass a written proficiency
examination and conform to the IRS rules of practice.
Other common abbreviations are:
IRC or code (The US Internal Revenue Code, the law or statutes
passed by congress, usually in the form IRC 61).
Reg or regs (The regulations interpreting the code published
by the US Treasury and/or Internal Revenue Service, usually in the
form Reg 1.61(a)(1)).
Rev Rule (Internal Revenue Rulings further interpreting the
regs or code, usually in the form 95-67).
Rev Proc (Internal Revenue Procedures IRS administrative
procedures about a specific subject or area, usually in the form
Rev Proc 95-3).
IRM (Internal Revenue Manual, the IRS employees manual setting
out how agents and others are to perform audits and examinations,
assess penalties, etc. Most of the manual is available to the
public, however, some sections are for internal use only).
Pub (IRS publications intended to assist taxpayers in
complying with specific sections of the IRC or in handling certain
type of transactions, usually in the form Pub 510).