Definition of grey knight in English:

grey knight

noun

Stock Market
  • A person or company making a possibly hostile counter offer for a company already facing a hostile takeover bid.

    • ‘The gray knights are essentially the scavengers of takeover attempts.’
    • ‘The new bidder, the gray knight, is not as preferable as the white knight, however, the gray knight is still a better option than the black knight.’

Origin

By association with black knight and white knight.