Accepting a plea deal is a criminal conviction. It’s called a plea deal because it’s a deal by which you plead guilty and waive your right to further argue against the charges.
(Edit: actually if I remember correctly, the vast majority of plea deals have the defendant pleading “No Contest” rather than “Guilty” because the former is not an admission that you actually did anything wrong just that you aren’t going to fight about it anymore. I’m not sure all of the situations it matters, but I believe it would matter in a civil suit regarding the act in question. That is, a guilty plea could be used against you, but the no contest plea could not.)