Salami technique works like this: If you take a whole salami sausage from someone who owns the thing and won't like the idea, the person will notice and will try to get it back. However, if you ask one slice of it, s/he might give that to you. This way, you can possibly ask for many, many, many, many slices - most of the sausage - and the owner will not notice that you stole most of it.
In computer cracking scene, this mostly applies to banking and other things like that. One bored bank computer administrator once, I heard, got large amounts of money by transferring all thousandths of pennies (left over when rounding other transactions) to his own account. A bank manager stole a million in small amounts over a long time. All these are just legends - but the point is, the security people will notice all large transactions but ignore small ones.