The regulations define weather flight conditions for visual flight rules (VFR) and instrument flight rules (IFR) in terms of specific values for ceiling and visibility. IFR means a ceiling less than 1,000 feet AGL and/or visibility less than three miles. Low IFR (LIFR) is a sub-category of IFR.

GUIDELINES
A person who applies for an instrument rating must:

• Hold at least a current private pilot certificate or be concurrently applying for a private pilot certificate with an airplane, helicopter, or powered-lift rating appropriate to the instrument rating sought.
• Be able to read, speak, write, and understand the English language.

You must have logged the following:

• At least 50 hours of cross-country flight time as pilot in command. At least 10 of these hours must be in airplanes for an instrument-airplane rating.
• A total of 40 hours of actual or simulated instrument time on the areas of operation listed in 61.65(c).
• At least 15 hours of instrument flight training from an authorized instructor in the aircraft category for the instrument rating sought.
For instrument-airplane rating, instrument training on cross-country flight procedures that includes at least one cross-country flight in an airplane that is performed under instrument flight rules. This flight must consist of:
• A distance of at least 250 nm along airways or ATC-directed routing.
• An instrument approach at each airport.
• Three different kinds of approaches with the use of navigation systems (Example: ILS, VOR, GPS, etc).
• At least 3 hours of instrument training that is appropriate to the instrument rating sought from an authorized instructor in preparation for the checkride within two calendar months before the examination date.