Designating the average number of eggs produced by a flock of hens in a particular laying period.
A hen housed average is based on the total number of birds in a flock at the beginning of a laying period. A hen-day average, by contrast, is based on the total number of birds at various points in the laying period and is typically higher than the hen housed average, as birds which have died since the beginning of the laying period are not included in the calculations.
1930s. From hen + housed, past participle of house, in e.g. eggs per hen housed; compare.