In the United Kingdom, and specificlly England (London), what is the
difference between a flat and a terrace?

I am looking at property report and it gives a breakdown of kinds of
properties in the area: flat, terrace, semi-detached and detached.

So what's the difference between a flat and a terrace?

Hello slugmeister-ga,

Thank-you for your question.

In the UK, a flat is usually a room (or number of rooms) within a
building being used by the same occupant.  It is equivalent to an
apartment in the USA.

"An apartment (or flat in Britain and most other Commonwealth
countries) is a self-contained housing unit that occupies only part of
a building. Apartments may be owned (by an owner-occupier) or rented
(by tenants)."
http://en.wikipedia.org/wiki/Apartment

A terrace is a row of houses in a street with common dividing walls. 
A terrace house is one of the units (or houses) within the row.

"In architecture and city planning, a terrace (..) is a style of
housing (..) where a row of identical or mirror-image houses share
side walls."
http://en.wikipedia.org/wiki/Terraced_house

The Wikipedia article above shows some typical terraced housing in the
UK (or London).  I believe they are called townhouses in the USA.

It is not uncommon (especially in London where housing is at a
premium) for terraced houses to be broken down into flats where one
tenant may rent one floor (room or rooms) and another tenant rent
another floor (room or rooms).

There is a good list of housing types (complete with descriptions) here:
http://en.wikipedia.org/wiki/List_of_house_types

If you require any further assistance please do not hesitate to ask
for clarification.

Thank-you for the 5-star rating and tip!  They are both appreciated.