That's called: "Oops! That never happens!"
It is impossible for the sun to come between the Earth and the moon. The sun is millions of miles farther away from Earth than the moon is!
Perhaps you are thinking of when the EARTH blocks the moon from receiving and reflecting rays from the sun. That is called a "lunar eclipse." Here's a site that talks about different types of lunar eclipses:
It's also possible you just have things reversed; maybe you're interested in the situation where the moon almost entirely blocks the sun's light from our view. This CAN happen, because the moon is closer to the Earth. It's called a "solar eclipse."
The moon is much smaller than the sun, but since it is SOOO much closer to us, when it comes between us and the sun, it almost completely "eclipses" (obscures from view) the sun and its light. (The sun's corona is visible during a "total eclipse.")
Here's a site that discusses solar eclipses and related concepts:
Hope this helps!