A bastard is someone whose parents did not marry or is something that has been changed or is not normal. In slang, a bastard is also someone who people do not like. (noun)
An example of a bastard is a child who does not know her father.
An example of something that can be referred to as a bastard is a song that has been poorly remade.
An example of someone who may be called a bastard is someone who routinely bullies others.