CARF stands for Central Altitude Reservation Function is the organization responsible for processing altitude reservations (ALTRVs) for military operations. These types of NOTAMs are designed to keep private air traffic clear of military operations, and to give authorization for military aircraft to conduct operations not normally allowed under standard ATC rules and regulations. Here is an example of a CARF NOTAM:
!CARF 01/109 (KZBW A0009/07) ZBW CARF NR. 111 ON CORONET EAST 019 LEG-3 MILITARY ACTIVITY ALONG THE ROUTE BETWEEN DOVEY ACK 15000-FL210 WEF 0701251609-0701251841
Not all altitude and airspace reservations start off with CARF, off-shore reservations or reservations where there is inadequate radar coverage may be issued as an international NOTAM like the one below:
M0493/06 - AIRSPACE RESERVATION ACTIVATED AREA OAK ALPHA 3907N 7153W 3841N 7155W 3820N 6957W 3830N 69W 37N 69W 37N 7240W 3715N 7240W 3757N 73W 3820N 7248W 3846N 7230W SFC- FL055 08 NOV 23:59 UNTIL 07 FEB 23:59 2007
These types of NOTAMs should be treated like Special Use Airspaces (SUA), you should avoid flying in the area described in the NOTAM while the area is active. Speaking of SUAs, the FAA has a great site for checking the coverage and status of SUAs at http://sua.faa.gov/. A careful check of both the CARF NOTAMs and SUA should help you stay clear of the fast-movers!