The problem is that many deleterious mutations are NOT selected out; they produce genetic disease that a person may simply have to live with.
Your ignorance is beyond the ken of mere mortals. Despite debating about evolution for years, you are still asking for the definition of terms like deleterious and selection.
Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)
I believe that a scientist looking at nonscientific problems is just as dumb as the next guy. Richard P. Feynman
If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass
I think a general definition of a deleterious mutation is where the organism is less successful at contributing offspring to the next generation than it would have been without the mutation.
This means there are varying degrees of deleterious. A mutation that causes failure to live long enough to reproduce means the organism contributes no offspring to the next generation. A mutation that shortens the life of an organism means it has a reduced period during which it can contribute offspring to the next generation. A mutation that makes it less competitive means it would be less able to look after its offspring, or less successful at finding a mate. And so forth.
Humans provide a poor example of the effects of less severe deleterious mutations because of family and social group support and because of modern medicine.