The current lineweight is the lineweight used for any objects you draw until you make another lineweight current.
All objects are created using the current lineweight, which is displayed in the Lineweight control on the Properties toolbar. You can also set the current lineweight with the Lineweight control.
If the current lineweight is set to BYLAYER, objects are created with the lineweight assigned to the current layer.
If the current lineweight is set to BYBLOCK, objects are created using the default lineweight setting until the objects are grouped into a block. When the block is inserted into the drawing, it acquires the current lineweight setting.
If you do not want the current lineweight to be the lineweight assigned to the current layer, you can specify a different lineweight explicitly.
Objects in drawings created in an earlier release of AutoCAD are assigned the lineweight value of BYLAYER, and all layers are set to DEFAULT. Lineweight assigned to objects is displayed as a solid fill drawn in the object's assigned color.