Off-lease (from a DELL standpoint anyway) simply means just that. They were leased to a company for a set amount of time, the company used (and abused them alot of times) and when the lease with DELL expired, they were re-allocated by DELL. Same concept with a leased vehicle that is being sold after being in service for so long.
Off-lease PCs are also going to typically carry an as-is warranty with them, simply meaning that if something breaks, you're responsible. When computers are taken in, they are put back to working condition (if the leaser sent them back non-working) and then sold. Usually it's a bottom-of-the-barrel type scenario.
The first link you posted for TigerDirect is indeed one of those types of computers.
The 2nd link for the DELL computer however is not unless it states as much.
The DELL Outlet is typically where older, refurbished models get sold off for a percentage of the original cost.
Don't let the term "refurbished" fool you though, when DELL takes a computer back, whether it be as a return from a customer or whatever, there are a large majority that have never been booted up the first time.
The minute it leaves the warehouse to be shipped to customer, it is no longer considered new. It has to be tagged as refurbished. The catch here is trying to figure out which ones have been repaired and which are brand new. Usually the price point will reflect this.