Summarized speech is revelation that does not contain enough information for us to know how to implement it. For example: "Perform the prayer!" does not tell us how to pray.
Elaborated speech is revelation whose implementation has been made possible by the revelation of additional information. For example: "Perform the prayer" is in and of itself "summarized," but when viewed together with the Prophet's Sunna, which specifies how to pray, it becomes "elaborated."