The term tolerance stands for the thing which is quite tolerated till a limit or you can for some time, and bug means is that if you don't know how to get around this, you may loose some of your work. But some bugs effected your some particular types  issues not the alls so, that types of Bugs called Tolerance Bugs which will ignore for some-time.

Those bug which doesnt have a important functionality, can be mark as defered.

The bug which will not affect on Aplication or performance, and can be done after some time.