Jamaica, Queens is what the entire area of southeastern Queens (the neighborhoods of South Jamaica, Cambria Heights, Laurelton, Rochdale, Springfield Gardens and Hollis) are collectively called by non-residents. But technically, Jamaica is really the busy area between Liberty Ave and Hillside Ave. It is the largest major hub in southeastern Queens and the second largest in Queens (after Main St. in Flushing) due to the Jamaica Ave. shopping strip, E/J/Z trains at Parsons/Archer, F train on Hillside, LIRR/JFK Airtrain at Sutphin Blvd. and bus terminals at Parsons/Archer and 165 St.
To address the previous posts, 50 Cent is NOT from Jamaica, but is from South Jamaica, which to residents, are two different areas. He was from 40 projects which is on the other side of Liberty Ave. Also, even South Jamaica isn't as bad as neighborhoods like South Bronx, East NY, Brownsville, Flatbush/East Flatbush, Far Rock etc. Jamaica isn't the greatest neighborhood but it's not the worst either. I go through Jamaica everyday (even at night) and not much has been going on, even when I'm alone. As with any area, be aware of your surroundings and you'll be fine.