When you hear the word "desecrate," it means to do something really bad and disrespectful to something that is supposed to be important, like a religious symbol or a special building.
Imagine you have a special toy that you love and care for. You keep it in a special place and you never let anyone else touch it without permission. Now, imagine someone comes along and intentionally breaks it or plays with it in a rough and careless way. This is kind of like what it means to desecrate something.
Some examples of desecrating might include vandalizing a place of worship, destroying a memorial or monument, or disrespecting the American flag. These things are considered very wrong and can be hurtful to a lot of people. It's important to treat important things with respect and care, just like you would with your favorite toy.