Definition - What does GHOST Bug mean?
The GHOST bug is a security vulnerability found in the GNU C Library (glibc) used by the Linux operating system. It was discovered by security firm Qualys in January 2015. According to Trend Micro, however, the affected library was already patched by May 2013.
Techopedia explains GHOST Bug
The flaw is found in the "gethostbyname" and "gethostbyname2" functions of the glibc library. These functions are used to resolve a domain name to its IP address. The GHOST bug can be exploited to create a buffer overflow, a vulnerability that allows an attacker to execute arbitrary code on an affected system, enabling the attacker to control the system. As the bug was already fixed in 2013, newer systems are not affected by this flaw. Moreover, the said functions are already obsolete, having been superseded by the "getaddrinfo" function.