After the smoke is gone is it harmful to you and those who don't smoke is that considered secondhand smoke?

Dont understand ?: If you test the air in an apartment where people smoke, residue of the smoke persists on the walls, furniture and everywhere else there is a surface in the apartment. In addition, it can be found in neighboring apartments where people are not smoking. This residue may be harmful to children who put everything in their mouth and can absorb toxins through the skin.