What is "culbert"

Culbert is a personal name that seems to have originated in Europe. The earliest records for this surname are found in Scotland, Ireland, and England. The use of surnames became necessary when governments introduced personal taxation. In England, heritable surnames started to form in the 11th century, and were common in most areas by 1400. The Poll Tax introduced in England in the 14th Century (considered a head tax) is probably the first time this common usage of surnames was documented.