A seat is the name given to the position a
M.P. holds in the
House of Commons in the
U.K.. There are 659
constituencies in the
U.K. so their are 659 seats to be filled by
M.P.s
(as of June 2001 elections)
There are 529 seats from
England, 72 from
Scotland, 40 from
Wales and 18 from
Northern Ireland.
There is one seat per constituency and only one M.P. can hold one seat. These seats don't all literally exist since there are a lot more constituencies/seats than there is room in the House of Commons. When all the M.P.s squeeze into the Commons they have to stand in the aisles etc. since there aren't enough benches to go round.
e.g. in an election the Conservatives may win a certain number of seats.