Sorry if my english is not perfect (after all its not among the two official languages we speak here. And still there's another language in my home additionally), but i would still guess, it should be pretty obvious: paying too much to your top players. So top-loaded cap structure is maybe better term?
The trend to spend extra millions to front/top players is obviously not resulting cups. In the end, what ypu can gain by having topmplauer instead of very good, is not enough to compensate the loss of having to replace good middle 6 player by an average rookie.
I know, many if not most thi k vice versa but results are are showing different story.
I'll give you the benefit of the doubt for English being a second language. In the future, "Front-loaded" references contracts where players were given a shit-ton of money at the start of their contract and next to nothing at the end with the understanding that they would likely retire before fulfilling those last few years.
It was basically tacking on years the players never planned on playing to lower their cap hit and, for the most part, was phased out with the 8 year term limits. Players like Marian Hossa (Developed an allergy right as his salary dropped to $1M/year) and Zetterberg (Suddenly couldn't bear his back pain anymore once his salary cut in half) are good examples.
Where I can't really give the benefit of the doubt is with what you actually meant, lumping Buffalo in with teams like Toronto who are top heavy in cap structure. For the rest of the decade, BUF will be paying their Top 3 players a whopping $25M. Coming from a fan of a division rival, they're going to be an absolute pain in the ass simply due to the depth they'll be able to afford.