definiens: shall mean the period commencing upon expiration of Research Program Term and ending on the earlier of ( a ) thirty - six ( 36 ) months later or ( b ) the effective date of [COMPANY] ’s termination thereof in accordance with Section 4.4 . 1 . For clarity, if [COMPANY] does not exercise its righ t pursuant to Section 4.4.1 to require NGM to conduct additional research and development of Tail Compounds / Targets, then there will not be a Tail Pe riod . Unless [COMPANY] terminates the Tail Period in accordance with Section 4.4.1 ( in which case the Ta il Period and the applicable Tail Year shall end upon the effective date of such termination and the re shall not be any new Tail Years after such effective date ), the Tail Period shall consist of t he following four ( 4 ) Research Program Years ( each a ): ( i ) Tail Year 1 shall begin on April 1 of the C alendar Year in which the Research Program Term ends ( such Calendar Year, the ) and shall end on December 31 of the End Year, ( ii ) Tail Year 2 shall begin on January 1 of the Calendar Year immediately following the End Year and end on December 31 of the same Calenda r Year, ( iii ) Tail Year 3 shall begin on January 1 of the Calendar Year that is the second C alendar Year after the End Year and end on December 31 of the same Calendar Year, and ( iv ) Tai l Year 4 shall begin on January 1 of the Calendar Year that is the third Calendar Year after the End Year and end on March 31 of the same Calendar Year