From The Jargon File (version 4.4.7, 29 Dec 2003):
flood
v.
[common]
1. To overwhelm a network channel with mechanically-generated traffic;
especially used of IP, TCP/IP, UDP, or ICMP denial-of-service attacks.
2. To dump large amounts of text onto an IRC channel. This is especially
rude when the text is uninteresting and the other users are trying to carry
on a serious conversation. Also used in a similar sense on Usenet.
3. [Usenet] To post an unusually large number or volume of files on a
related topic.