expedition = "a journey or voyage undertaken by a group of people with a particular purpose, especially that of exploration, scientific research, or war" - Google
This definition applies to the context in which "expedition" is used in the sentence.
expedition = b.) journey
It would be an example of imagery, which is the figurative device that focuses on vivid details. Hope this helps! :)
A.) I was thrilled to find my keys they had been lost since yesterday.
This is a "fused sentence" or also known as a run-on sentence.
