LAND is an abbreviation for Local Area Network Denial-of-service. LAND is a DoS attack that essentially causes a target host to get stuck in an endless loop replying to itself.
LAND attacks start with the sending of a crafted packet to the target host. This packet spoofs the source IP address so that both source and destination IP address fields are those of the target. Also, the crafted packet sends a TCP SYN request on an open port. The effect is to get the host caught up endlessly trying to reply to its own SYN requests.
Reference: http://insecure.org/sploits/land.ip.DOS.html