The abbreviation kyr means "thousand years".
Kyr was formerly common in some English language works, especially in geology and astronomy, for the unit of 1,000 years or millennium. The "k" is the unit prefix for kilo- or thousand with the suffix "yr" simply an abbreviation for "year".
Occasionally, the "k" is shown in upper case, as in "100 Kyr"; this is an incorrect usage. "kyr" itself is often considered incorrect, with some preferring to use "ky".