A more thorough explanation:

A lesser crime, also known as a lesser included offense, is a crime that is necessarily committed in carrying out a greater crime because the greater crime contains all of the elements of the lesser crime. For example, if someone is convicted of murder, they are also necessarily guilty of battery because the elements of murder include the offense of battery.

However, a jury cannot convict a defendant of both a greater and lesser crime for the same conduct. Instead, a court may instruct a jury to convict the defendant on a lesser crime even if they are not convinced beyond a reasonable doubt that the defendant is guilty of the greater crime.

Prosecutors sometimes decide to charge a defendant with a lesser crime to increase their chances of securing a conviction, rather than risking an acquittal at trial for a greater crime. Prosecutors also use lesser crimes to encourage plea bargaining by offering to reduce a charge from the greater offense to the lesser offense in exchange for a guilty plea.

For example, if someone is charged with robbery, which is a greater crime, they may also be charged with theft, which is a lesser crime. If the jury is not convinced beyond a reasonable doubt that the defendant committed robbery, the court may instruct them to consider the lesser crime of theft instead.

Another example is if someone is charged with assault with a deadly weapon, which is a greater crime, they may also be charged with simple assault, which is a lesser crime. If the prosecution is not able to prove that the defendant used a deadly weapon, the court may instruct the jury to consider the lesser crime of simple assault instead.