It means opened by someone. Before it was closed, now it is open. Opened road - They finished fixing the road so now it is open. (Before it was closed.) Slightly opened - The mouth is open. The focus here is to imagine the person with his mouth open! :o (Maybe he is curious, scared, lazy, etc.) Opened package - Before it was closed but someone opened it.

Past tense verbs can be used as adjectives. This is used to describe an object which the action applied to. Examples: This car crashed. == This is a crashed car. This vase cracked. == This is a cracked vase. This test was graded. == This is a graded test. This also works with present tense verbs that end in -ing. This girl is walking. == This is a walking girl. This bear is frightening me. == This is a frightening bear. This light is flickering. == This is a flickering light. I hope this helped :)