No, it's one of many PE strategies. Almost all private equity firms utilize leverage in some form, but it's not universal and certainly not as extreme in all cases as the LBO shops.
LBO is how the PE firm finances the acquisition. Think of almost exactly like a mortgage. The bank ( = investment bank) doesn't want to maintain/manage the house ( = company) so they help fund the acquiring cost. Typically it's 50/50 (50% the PE firm uses its own fund and 50% it uses a loan from an investment bank "mortgage).
Post close, they might utilize a credit facility (usually a bank loan) where they can put debt on the company's books for specific initiatives (add-on acquisitions, hiring, etc.). There are some huge advantages to this because they usually can get loans at way better rates than a company could get if they went to a bank and got an SBA loan, venture debt, etc.
Today I would guess it's most associated with the Toys R Us and Sears failures, but surprisingly no one tends to talk about the Best Buy LBO for some reason...