Okay kiddo, think of the world like a giant ball. On that ball, there are imaginary lines going up and down called meridians. The 105th meridian east is a specific one that goes from the North Pole all the way to the South Pole, passing through different countries like China, Vietnam, and Australia.
This line helps us know where we are on the globe, just like how you use street signs to know where you are in your neighborhood. And if you live or visit somewhere along this line, you might notice that things like time zones and weather can be different from places on other meridians.
So, the 105th meridian east is just one of many lines that help us understand our planet and where we are in it. Cool, huh?