There was an interesting article in Rural Delivery this month about the whole biosecurity/backyard flocks thing. I checked their page but they don't have the article online. I picked up my copy at the Co-op feed store, not sure where else it's sold.
I'll do my best Mary. I think you don't know it because it is a newish jargonny word and like most jargonny words is meant to make those that use it feel smart. It means keeping your biology clean - uncontaminated by disease - it is a good idea for instance to not invite people into your hen house because they might be carrying bio-contaminants inadvertently or vertently(!) (bio-terroists) on their shoes or in their clothing. That would be securing your hen house against bio-problems or problems of a biological origin - ie - micro-organisms etc... It also means keeping wild bird flocks from coming into contact with your flock because they may carry diseases like avian flu and so on. Personally, for a back yard flock you could get to heavy about this in my opinion. I think if you are selling eggs and chicks and pullets you probably need to be more careful than if they are for your own use. But I'm sure there are other valid opinions out there.
Just sounds like sensible care to me. Thanks for the explanation, it is a word I will throw around at hubby, make him think I am just soooo intelligent. LOL.