imageCLASS LBP246dw Difference between bond and plain paper

[Gailinda]

I have the black toner laser printer Imageclass LBP 246dw.  What is the difference between bond and plain paper type?  The tray settings are:

Bond 1. 16-19 lb   Bond 2   20-27 lb.    Bond 3.  28-31 lb.

Plain 1.  17-19 lb.  Plain 2. 20-23 lb.   Plain 3. 24-28 lb.

What determines whether a paper is bond or plain?  The packaging only says for laser printer and the weight.