What it means
The first digit runs from 0 to 6. A 6 means dust-tight. The second digit runs from 0 to 9. A 5 means protection against water jets, 6 against powerful water jets, 7 against temporary immersion, and 9 against high-pressure, high-temperature spray. So IP66 means dust-tight and protected against powerful jets, and IP67 adds short immersion. The two tests are separate, so a product may be marked IP66/IP67.
A rating applies to the enclosure as tested, with its glands and connectors closed. Poor cable entry on site can defeat it.
How it applies in India
Outdoor traffic cameras in India face monsoon rain, dust storms, high heat and pressure washing at toll plazas. IP66 or better is the usual requirement for a roadside camera. Ask for the test report, not only the datasheet line, and check the rating covers the IR illuminator and any external connectors. Pair the IP rating with an IK rating for impact.