what is the meaning of this sentence :
often,cats that end up in shelters have been abused or abandoned.
A shelter is a place where unwanted or homeless pets are taken to stay while they await adoption.
Unfortunately, many of the pets (dogs and cats) that end up in shelters have been abandoned by their owners because they simply didn't want them anymore. Some of those pets have been abused - unfortunately there are some sick, twisted people in the world who do things like setting dogs or cats on fire, or beating them with baseball bats, or throwing them out of moving vehicles.