Force Breaks are a gameplay mechanic that were introduced in Guilty Gear XX Λ Core.
Identical to Overdrives, Force Breaks are moves that can be done at the expense of Tension (albeit 25% and with a brief white circle-glow flash with the same sound Overdrive start-up flash sound effect from before Λ Core).
Force Breaks are usually done with a specific input ending with (though via prior to Λ Core, there still exist some special moves that are not Force Breaks that use this button). These are essentially identical to EX Special Moves in other fighting games such as Darkstalkers and Street Fighter (being meter-costing moves that are moreso enhanced special moves as opposed to actual supers), albeit a number of them are their own original attacks different from the rest of the character's kit, mainly due to some of them being past moves being converted into Force Breaks.
Every character within the Λ Core entries has at least one Force Break, with each Force Break being unique to the character as well as the amount one has. For instance, there exist Force Breaks such as Baiken's Baku (which are prior moves revamped into being a Force Break). Though there also exist Force Breaks such as Axl's Force Break-version Axl Bomber that are just an enhanced version of a special move (playing more into the role of an EX Move as aforementioned).
Additionally, there are Force Breaks that can only be done when inputting a special move (e.g. Jam's FB-version Hyappo Shinshou) or even as a followup to another Force Break prior (e.g. from Sol's FB-version Fafnir to Tyrant Rave). Some moves (e.g. Johnny's Jackhound) as aforementioned are past attacks converted into being Force Breaks.
Some Force Breaks despite the cost being 25% Tension in general, even act as Overdrives with the exact same start-up flash (and as a result, disable the victim's usage of a Psych Burst and also can count towards Overdrive K.O.s), though these are only followup Force Breaks and never standalone ones.
Even then, a number of offensive Force Breaks often deal solid damage just short of an Overdrive, though both offensive and non-offensive Force Breaks much like EX Moves in general have other forms of utility central to a character's gameplan.