freebsd biord in top

It is state, like deadlock, when kernel is waiting for disk.
wdrain is like this.

These both are undocumented states of kernel.

If you catched biord or wdrain (or ffsfsn, or some other strange status (that is not kserel, CPU, select or other statuses normally displayed in top), most probably you have serious problems with i/o of your application.