1) noun. Stuff that is made up for the purpose of placating someone, or passing an exam, or getting elected to office. Most often false or ridiculous.
2) verb. To generate bullshit.
3) interjection. Accusing someone of bullshitting.
4) adjective. Identifying or suspecting something as bullshit.
In all usages, the term can be shortened to "bull" or "BS".
1) My essay was complete bullshit.
2) Man, I gotta learn to bullshit properly if I want to pass this English exam.
3) "I was sick all last week!" "Bullshit!"
4) That is such a bullshit answer.