That is, lasting or continuing for ages, or periods exceeding any historical measurement of time. The origin is Biblical, the Hebrew word olam (עולם), with an array of meanings centered around the world, including the physical planet, the states if the world, a domain of someone's life or learning, and the temporal duration of one's lifetime or the lifetime of the world. In the Torah, it most often appears in the form l'olám, in the sense of roughly "to the extent of the world," which almost always carries the temporal meaning -- and it's in the Old Testament that English-speaking Christians met it. contemporary English-speaking Jews, however, most likely know the word from tikkun olam, the responsibility Jews have to "repair the world" by performing mitzvot and, for Reform Jews, doing good works. (A word chosen for those celebrating the birthday of the world this week.)
The millennium clock may not be olamic, but ten-thousand years is pretty darn longer than my lifetime.