A block is a collection of objects you can associate together to form a single object, or a block reference. You can insert, scale, and rotate a block reference in a drawing. You can explode a block reference into its component objects, modify them, and redefine the block. AutoCAD updates all future instances of that block reference based on the definition of the block.
Blocks can be defined from objects originally drawn on different layers with different colors and linetypes. You can preserve the layer, color, and linetype information of objects in a block. Then, each time you insert the block, you have each object within the block drawn on its original layer with its original color and linetype.
For more information about working with blocks, see “Create and Insert Symbols (Blocks)” in the User's Guide.