Yes- it rhymes with Raisonet! I discovered this new term in NYC land of the luxury co-op/condo experts. Further research shows that it is very common lingo in the UK and can represent a one level (flat) or multi-level townhouse style home.
As a term used to sell street level homes in one of the world's busiest cities, maisonette will likely start to appear locally as well - particularly for luxury buildings. Granted - while the idea of living above it all in the penthouse sounds wonderful - apparently there are drawbacks that maisonettes do not have.
1. Noise: Curiously - you may not realize that street level noise travels upward wiht minimal loss of quality and volume. Apparently it hits the sie of the building and changes course intact giving upper floor dwellers no escape from honking horns and sirens.
2. Time: When pitching a maisonette - it is key to ask the buyers how how of their life they would like to spend waiting for and standing in the building elevators. Maisonettes generally avoid all of these delays woht direct secure acces to the street level.
3. Value: Maisonettes may have a lower price than upper level units and may also have a lower share of the association fees.
On the cons - improper sound proofing between floors can result in your knowing too much about your neighbor's lifestyle - but this can apply to all floors not just non-penthouse homes.