An eclipse of the sun is an occasion when the moon is between the earth and the sun, so that for a short time you cannot see part or all of the sun. An eclipse of the moon is an occasion when the earth is between the sun and the moon, so that for a short time you cannot see part or all of the moon.
If one thing is eclipsed by a second thing that is bigger, newer, or more important than it, the first thing is no longer noticed because the second thing gets all the attention.