Coin manipulation is when someone tries to make money or gain an advantage by controlling how much a coin is worth.
Imagine you have a toy car that you really like. One day, your friend wants to play with your toy car too, but you don't want to give it to them. So, you pretend that your toy car is magic and say that if your friend gives you all their candy, the toy car will turn into a real car that they can keep forever.
Your friend really wants a real car, so they give you all their candy. But, of course, the toy car doesn't turn into a real car because it was just a trick. You got all your friend's candy for nothing in return.
This is similar to what can happen with coins. Some people might try to make people believe a coin will be worth a lot of money in the future, so they buy a lot of it. Then, when the price goes up (because lots of people are buying it), they will sell it for a profit. This is called "pumping" the coin.
But, sometimes people will try to do the opposite. They might convince people that the coin is not worth anything, so they all sell it. Then, the price goes down and the people who convinced others to sell it will buy it themselves at a lower price. This is called "dumping" the coin.
Both pumping and dumping can be really bad for people who invest in the coin. They might lose a lot of money if they buy when the price is high and then it goes down. It's important to do research and not just believe everything you hear about a coin's value.