ClassB

ClassB is a label used in several classification schemes to denote a middle or intermediate category. It does not refer to a single standard, but to different systems where B marks a mid tier.

In networking, Class B refers to mid-range networks within the historical IPv4 classful addressing scheme. The first octet ranges from 128 to 191, with a default subnet mask of 255.255.0.0. Each Class B network supports up to 65,536 addresses, and there are about 16,384 such networks. Classful addressing has largely been superseded by CIDR and variable-length subnetting, but the concept remains a reference in historical discussions. A private Class B block exists in the range 172.16.0.0/12.

In vehicle licensing, Class B denotes a license category used in various jurisdictions for operating heavier or larger vehicles. This often includes single vehicles above a specified weight and, in many places, certain types of buses or large trucks. Requirements typically include written and road tests, vision screening, and medical certification, with exact definitions and restrictions varying by country or state.

In electromagnetic compatibility standards, Class B refers to equipment intended for residential or light commercial use and is subject to stricter emission limits than Class A industrial equipment. Standards from bodies such as CISPR and the FCC characterize Class B limits for radiated and conducted emissions to minimize interference in nonindustrial environments.

In astronomy, Class B denotes a spectral class of hot, blue-white stars (B-type), characterized by high surface temperatures and distinct spectral lines.