The verb merge means to seamlessly join something. For example, when you merge onto the highway, you need to smoothly join the traffic, forgetting everything you learned riding the bumper cars at the fair.
If two or more things become one, they merge. If your favorite deli, The Cheese Stop, merges with a sandwich shop called Chez Lui, the two restaurants might also merge their names, becoming Chez Cheese. You can also use merge when things only appear to blend. You know it's time to go to sleep when the words in your book begin to merge together.