What is 定力? Context: This guy was cursing about his lack of that. 2. It's a Xianxia Google just says it's one of the 5 forces/power in Buddhim :/
定 (dìng): to set; to fix; to determine; to decide; to order 力 (lì ): power; force; strength; ability; strenuously I thought perhaps "... lack the strength to decide."
AFAIK, it's a little bit of all of the above. Like @Ram5 said, it's the ability to fix, or stay determined, so both fortitude and concentration also play a role in it. It's the ability to stay determined and focused, unwavering, unyielding to distractions/temptations. In a sense, perhaps self control or self restraint would be a more fitting term for it. For example, if an apprentice monk is meditating, and a cute girl came over and whispered seductively into his ears, and his ears twitched and his eyebrows frowned slightly, his master would come over and smack him over the head and say that he lacked "定力".