Most exchanges charge for access to their real-time market data (quotes and trade information).
The charges for professional users are considerably higher than for non-professional use. Accordingly, many exchanges, and US exchanges in particular, have a detailed questionnaire that they require users to complete in order to qualify for the lower charges.
If you wish to access real-time data for any of the following data services (AMEX, CME, NYSE, NASDAQ, OPRA or U.S. Securities Snapshot & Futures Value Bundle), you must fill out this questionnaire and re-affirm it annually.
More information about Professional vs. Non-Professional data use can be found at various knowledge base articles: