Original: The meet-in-the-middle attack uses a space-time tradeoff to find the cryptographic key in only  encryptions (and  space) versus the expected  encryptions (but only  space) of the naive attack.
Simplified: The meet-in-the-middle attack attack uses a space-time tradeoff to find the cryptographic key in only  encryptions (and  space) compared to the expected  encryptions (but only  space) of the normal attack.