History: What does a low-pass filter do?

What does a low-pass filter do?

• It reduces or eliminates content outside of a specific frequency range.
  That's a band-pass filter.
• It reduces or eliminates low-frequency content.
  That's a high-pass filter.
• It reduces or eliminates content within a specific frequency range.
  That's a band-reject filter.
• It reduces or eliminates high-frequency content.
  Excellent!