What Long Island really is all about is difficult to pin down. It's hard to even agree on what Long Island is. Ask someone from the area and they will tell you that Long Island is Nassau and Suffolk county. A person from Brooklyn would never consider themselves a "Long Islander". But physically, Long Island encompasses four counties including parts of NYC. Going west to east they are Brooklyn and Queens which are part of New York City, and Nassau and Suffolk. The entire island is 118 miles long (it is a long island, the longest adjoining the continental US) of which 85 miles is Nassau and Suffolk. At its widest point, the island is about 20 miles wide. Living on Long Island, it is very easy to forget that you live on an island (at least until you want to get off it).
The population of Long Island is larger than most cities. Including Brooklyn and Queens there are about 8 million people on Long Island. The population of Nassau and Suffolk is about 2.8 million. Generally, the further east you go, the less populated the island is (except for the Hamptons in the summer). For those who are interested, the population density of Nassau County is 4,655/mi²!
Long Island is often thought of as a "bedroom community" for New York City and to some extent that is still true although most people on Long Island don't work in NYC. Long Island is made up mostly of single-family detached houses. Median household income on Long Island is pretty high (although the cost of living is high) and the education system is generally excellent. Many top-ranked colleges are on Long Island. Many top-ranked hospitals are here as well.
The weather on Long Island tends to be moderated somewhat by our proximity to the ocean but we have definitely have four distinct seasons. Did I mention we have 1,180 miles of shoreline including some of the nicest public beaches in the country?
Some Info about Long Island:
Special bonus picture from my front door: