An IK rating states how much mechanical impact an enclosure survives, on a scale from IK00 to IK10. It describes resistance to a blow, not to water or dust, which the IP rating covers. A high IK number is useful on cameras within reach in public or unsupervised areas.
IK and IP are different tests and both appear in a datasheet. Mixing them up leads to a camera that survives a jet wash but not a thrown bottle.
What the IK scale measures
The IEC 62262 scale rates impact energy in joules against the enclosure. IK10, the top of the range, is rated for 20 joules of impact.
Choosing a rating for the site
Reachability sets the requirement. A dome above a loading door may be fine at IK08, while a camera at head height in a school corridor justifies IK10.
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