With V18, the concept of "Blocks" was introduced which parallels AutoCAD's Block functionality and can in fact use any existing AutoCAD Block libraries. Symbols also still exist, but where blocks are individual sets of user defined geometry and several defined blocks can be stored within a single Draft file (the file is the library container), a Symbol is comprised of whatever graphics exist in a single Draft file, so for each symbol you create, it is saved as a Draft file. Symbols do have some options that the Blocks do not. A symbol can be placed as graphics (no remeberance of the fact that it was a symbol), linked (associative to the original definition. Think Write Blocks from ACAD), embedded (each instance in the drawing can be individually edited without affecting the others in that drawing), and shared embedded (editing one in the drawing affects all others in the drawing), or as a block. Blocks work like Symbols placed using the "shared embed" option so editing one block in the drawing makes all other update to match.