You were arrested for shoplifting a few years ago but never charged Is this considered a detainment?

In general, "detainment" isn't a legal issue. Generally, even being "arrested" isn't an issue. According to the prevalent legal definition, detainment means, under security control, under suspicion BUT w/o proof. Under arrest, generally means some means of proof. You can be detained, basically at the wishes of the security forces, which is legal, but the conditions are not as stringent as an arrest. Only applies to my knowledge of US law.