Misdemeanors are classified from 1 – 4 or A – C, depending on the state. 1 (and A) define the most serious offenses, and 4 (and C) define the least serious.
To expunge a conviction from your criminal record, the court considers the time passed since arrest/conviction, the severity and nature of the crime, your previous criminal record, and other relevant factors.
A plea bargain is a negotiation in which the defendant pleads guilty to a lesser charge in order to get a more serious charge dropped. An experienced attorney can help you understand what is being offered.