...DSC you know better than that... those Apexi N1 Pros are
NOT "typical coilovers"! <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt='
'> They're super sexy coilovers.
In tuner language though, coilovers mean exactly what DSC said, rather than a (simple) coilspring-over-shock set up as is found on stock 240sxs (and many other cars.)
A few things to note though, when looking at coilovers: Some have dampening adjustability while others do not. The specifications will tell you whether or not yours (or the ones you're looking at) do.
Nice/proper performance coilovers run between US$900 (bare bones, no pillow uper and non-adjustable dampening, but still ride-height adjustable) and US$2,800 (complete race coilover with 50mm piston, remote oil/gas (?) 'reservoir', 14kg/mm springs 24 way adjustability and height adjustability w/out affecting shock travel)... most will fall in the 1,200 to 2,000 range, though.
Also, nicer coilover sets (read: more expensive) also come with the upper mount, which is known as a pillowball mount or pillow upper mount. This is included in most coilovers EXCEPT Tein Type HA, Tein Type HR and Apex'i Worldsport (and a few others).
HOWEVER! These days there are more and more wannabe-coilovers, which are simply coilsprings with an upper seat and an threaded (adjustable) lower... "tube". These are NOT true coilovers! Most of these are made by gay butt loving people (like APC and Arospeed) who have no idea about performance tuning. These cost in the neighbourhood of $200 USD, but are worth closer to $20. They also require custom fabrication and work to the car and possibly the shocks that they're going on.