A plea offer is a proposed resolution in any given case. Generally speaking, the prosecutor will make a plea offer in each case that would allow for the Defendant to accept responsibility for the crime committed, and be punished for committing it. An overwhelming majority of criminal cases are resolved by plea agreement each year.
There are many reasons plea offers are made, to include (1) judicial economy, (2) wishes of the victim/victim's family, and (3) to avoid the uncertainty and cost of trial.
Before a plea offer is made to a Defendant, the prosecutor responsible for the case examines the facts of the case, the Defendant's criminal history, the victim's opinion, the general opinion of the community/how the community feels about the particular type of offense.