What does O.s. mean on the household exam. Is this one of the parents sons?

David A. Peterson

What does O.s. mean on the household exam. Is this one of the parents sons?

https://www.familysearch.org/ark:/61903/3:1:3Q9M-CSG4-QS9K-Q?cc=2790465&personaUrl=/ark:/61903/1:1:QLP3-S39F

Heidi Kuosmanen

O.s. means oäkta son, illegitimate son.​

Frithiof Joachim is Idasson (Ida Charlotta's son)​