Answer:

The term "incubator eggs" is applied to eggs from a medium grade of standard bred birds.

Large breeders of high grade stock usually have a number of breeding birds that are not fine exhibition birds but still are standard bred stock, the progeny of the best birds and just as suitable for those who do not care particularly for a high standard of exhibition excellence.

These eggs are sold cheaper, usually from $5 to $10 per 100, and are called incubator eggs.