A more thorough explanation:

First degree murder is when someone intentionally kills another person with planning, deliberation, or willful intent. There are two types of first-degree murder: premeditated intent to kill and felony murder. This definition will focus on first-degree murder involving premeditated intent to kill.

It's important to note that the exact definition of first-degree murder varies by jurisdiction. In most places, first-degree murder involves premeditation and deliberation, while all other intentional murders are defined as second-degree.

A premeditated intent to kill means that the defendant had the intention to kill and spent some time thinking about it before carrying out the act. This is different from killing on a sudden impulse. Courts look for evidence that the defendant deliberated and formed the intent to kill prior to the act of killing.

Some factors that indicate premeditation and deliberation include lack of provocation from the victim, actions and words of the defendant before and after the killing, any threats from the defendant before and/or during the killing, whether the victim and the defendant had a poor history, whether there was an additional lethal attack after the victim was already helpless, evidence of brutality, and the nature and number of wounds.

For example, if someone plans to kill their spouse and buys a weapon, researches how to use it, and waits for the right moment to carry out the act, this would be considered premeditated first-degree murder. On the other hand, if someone gets into a heated argument with a stranger and impulsively kills them, this would likely be considered second-degree murder.