There are basically three types of encounters citizens have with the police; a first tier, a second tier, and a third tier encounter.

A first tier encounter essentially is the type of encounter you could have with anyone on the street. For example, if I saw you on the street, I could walk up to you and attempt to strike up a conversation. You on the other hand could speak to me or simply walk away.

Police can do the same thing. They can attempt to communicate with you but if you didn't want to talk, you could simply walk away since there is no formal investigation and no criminal arrest. If they detained you, searched you, found contraband (usually drugs) and decided to arrest you, the chances are good that your case will be thrown out since this was a first tier encounter and you simply exercised your rights.