What is the definition of a deliberate and premeditated first degree murder?

" ' "A verdict of deliberate and premeditated first degree murder requires more than a showing of intent to kill. [Citation.] 'Deliberation' refers to careful weighing of considerations in forming a course of action; 'premeditation' means thought over in advance. [Citations.]" ' " (Mendoza, supra, 52 Cal.4th at p. 1069.) "An intentional killing is premeditated and deliberate if it occurred as the result of preexisting thought and reflection rather than unconsidered or rash impulse. [Citations.] However, the requisite reflection need not span a specific or extended period of time." (People v. Stitely (2005) 35 Cal.4th 514, 543.)