Jitsu is a term, used in isolation almost exclusively as a name of style of jujutsu practiced by the Jitsu Foundation - a British martial arts association.
'Jitsu' is western misspelling of 'jutsu' - a Japanese word translating to 'art' or 'skill'.
The unarmed fighting style Jitsu refers to is often spelled several different ways: most properly 'jujutsu,' but often 'Ju-Jitsu' or 'Jiu-Jitsu.'
Ju translates to 'Gentle','Soft', 'Pliant' or 'Adaptable'.
Thus Ju-Jitsu means the 'gentle art' as opposed to just Jitsu meaning 'Art', which by interpretation could be a little misleading.