Game design:

[insignificantly]

Your application should be supported by relevant documents that demonstrate your range of design skills, such as concept work, structure, mechanics and behaviour.

this is on the website of a game development company, thats looking for a game designer. i'm not trying to get the job. i just want to know what concept work, structure, mechanics and behaviour means.
mechanics is something like gameplay right? what are the other 3? and are there some other words that fit in the same category that game desicgners should know? im a beginning game designer, and want to make a profession out of it.