A stereotype is something that is used inherently by all people to help them determine where a person, an experience or an object falls in the realm of life and can be a good thing when it helps people to separate men from women or a snake from a twig. Stereotyping is not always "wrong," and, in some cases, it is a natural part of life.
It is also necessary for the mind to work properly and for the human brain to be able to perceive, process, store and then recall that information when needed. The problem stereotypes begin when people use them for things other than something as simple as distinguishing a door from a window. People sometimes use stereotypes in racial, religious, political and other ways that can provide an unfair basis against someone.
An example of a negative stereotype would be judging someone based on the color of their skin. This is called racism. Someone who was using a stereotype might say that a certain race of men are often criminals. This is an unfair stereotype.
Therefore, stereotypes can be both bad and good things. They will never be able to go away completely as humans need stereotypes to help them with processing information. The goal is to not use stereotypes in a negative way to discriminate against other people.