the back yard

Backyard is a space or an area that is physically and or metophorically close to us and well known. At least closer to us than the outer limits of reserach.

A common phrase is "this research is cutting edge" means at the furtherest reach of our knowledge.

"cutting edge" could be assumed to be opposite of "back yard".

In the States, a "back yard" is an area--usually behind the house--for outdoor, family activities.

Since the owner of the house takes care of cutting the grass and all other aspects of landscaping and the family spends a lot of time there, that family is as informed about the back yard as they are about any of the rooms in the house.

Now and then,researchers retreat from the trackless jungle at the edge of knowledge and set up camp in familiar territory.such more expeditions do not often yield surprises,but it is always reassuring to know that the back yard looks much as we though it did.
what is the meaning of the last sentence? especially"the back yard"

MEANS

Once in a while, researchers stop doing work in unknown areas and turn their interest to subject areas that are familiar. Such research does not bring new discoveries, but it gives us comfort to know that what we are used to has not changed.