Imagine you have a big ball, like a beach ball. This ball is the Earth, where we live. Sometimes, people like to measure things on the Earth to help them find places or figure out how fast things are moving. One way they do this is by using lines that go all the way around the Earth. These lines are called meridians.
Now, let's focus on one specific meridian. It's called the 115th meridian west. That means it's a line that starts at the North Pole and goes all the way down to the South Pole, and it's 115 meridians away from the line that was chosen to be the "prime meridian" (that's a fancy word for the one that's used as a reference point for measuring everything else).
To make it easier to understand where things are, people have divided the Earth up into different parts. One of these is called a time zone. It's kind of like a big slice of the Earth that all has the same time. The 115th meridian west is an important one for time zones, because it's where the time changes if you go from one time zone to the next. For example, if you live in a place that's on the west side of the 115th meridian, you might be in one time zone, and if you travel to a place on the east side of the 115th meridian, you might be in a different time zone.
So, to sum it up: the 115th meridian west is one of the lines that goes around the Earth, and it's important because it marks where different time zones start and end.