Something immeasurable can't be measured or quanitified. It's too vast.
When you measure something, you check how long it is, how much it weighs, or some other measurable aspect. If something is immeasurable, then measuring is impossible. The numbers of stars in the sky is immeasurable: we can't know how many there are. The number of grains of sand on a beach is immeasurable: they can’t be counted. This word means more than a lot. There are a lot of countries in the world, but they're not immeasurable.