A Light Head and a Heavy Head
The Alter of Kelm explained the terms kallus rosh (irreverence) and koved rosh (decorum) as plain translations. Kallus rosh means having a light head, and koved rosh means having a heavy head. A person whose head is full of wisdom does not turn it sideways and does not laugh readily. A layabout is seen at once for what he is, because his movements show that nothing weighs him down. His head is simply light, and at every rumor and every slight noise it wags.
Source: Rav Yeruchom's discourses, Da'as Torah, vol. III, 117