lg is the common mathematical symbol for the
logarithm to the
base of 2.
The unit of lg x, in
number theory, is commonly known as a
bit. As such, it can commonly be used in
computer science, for example, when analyzing the height of a
binary tree, using lg x is helpful since there are two branches per
node. Using
O notation, lg x can be used instead of log x, since they differ only by a
constant.
It can also be written as log_2 x, read as the
logarithm to the
base 2 of x.