The word "milenium" (also spelled "millennium") comes from the Latin words [mille annum](javascript:void(0)), meaning "thousand years." It is a unit of time that equals 1000 years. This period is often used in historical and calendar contexts, marking a span of a thousand years or a thousand-year anniversary. For example, the first millennium AD lasted from year 1 to year 1000, the second from 1001 to 2000, and so on. Thus, 1 milenium equals 1000 years.

Here is a summary for clarity:

Term| Meaning| Duration
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milenium| [ tysiąclecie](javascript:void(0)) / millennium| 1000 years

So, "milenium" or "millennium" means a period of 1000 years.