denial-of-service attackn. Computers A malicious attack on a network resource that prevents legitimate users from accessing the resource, typically implemented by initiating an overwhelming number of spurious requests for service. Also called DoS attack.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.