inholiday泛指放假,但说话人说话的时候并不在放假.

　　如,i'dliketostaywithmyfamiliesinholiday.

　　intheholiday指特定的假期,根据上文的延续.

　　如,Christmasisaspcialholidayinwesterncountries.Intheholiday,peopleusuallystaywiththeirfamilies.

　　onholiday处于放假的状态

　　如,i'monholidaynow.类似有onduty上班中

　　另外补充一下,如果你前面曾经提起过某个节日,而现在针对这个节日说on,就要用ontheholiday,特指在这个节日.否则,用onholiday.