Deadlock is a situation when two processes, each having a 
lock on one piece of data, attempt to acquire a lock on the 
other's piece. Each process  would wait indefinitely for 
the other to release the lock, unless one of the user 
processes is terminated. SQL Server detects deadlocks and 
terminates one user's process.

A livelock is one, where a  request for an exclusive lock 
is repeatedly denied because a series of overlapping shared 
locks keeps interfering. SQL Server detects the situation 
after four denials and refuses further shared locks. A 
livelock also occurs when read transactions monopolize a 
table or page, forcing a write transaction to wait 
indefinitely