According to USCIS, extreme hardship is defined as “to be considered %22extreme,%22 the hardship must exceed that which is usual or expected. %915%93 But extreme hardship need not be unique, %916%93 nor is the standard as demanding as the statutory 'exceptional and extremely unusual hardship' standard that is generally applicable to non-lawful permanent resident cancellation of removal%22.
To prove extreme hardship in a case, there are many different paths to prove extreme hardship. or more information about extreme hardship and what factors are considered in determining it, please see this section of the USCIS policy manual.