The sexist definition in the dictionary describes a sexist as a person who shares sexist beliefs and participates in sexist behaviors. Sexist beliefs are beliefs that revolve around sexism. The word sexist can describe the nature of a comment or gesture, as well.
So how long do they typically last? Well, standard copper plugs are said to last anywhere from 10,000 to 20,000 miles (16,093 to 32,187 kilometers), while more expensive iridium or platinum spark plugs can last 60,000 miles (96,561 kilometers) or more [source: Spark plugs UK].
Spark plugs use a ceramic insert to isolate the high voltage at the electrode, ensuring that the spark happens at the tip of the electrode and not anywhere else on the plug; this insert does double-duty by helping to burn off deposits.