W2 means an employee, from a wage standpoint it means your employer must pay for half your social security and medicaid.
1099 means a contractor, which means you are responsible for those.
There are many other differences, but usually when talking about wage the 7.5% is the big one.
w2 = waged.. the employer withholds tax and also pays half of some taxes that you need to pay
1099 = independent contractor.. you get the full amount but you pay taxes end of the year
1099 = 15% more in taxes you have to pay on the revenue you earn from that income source