Directory Structure
From GhostBSD Wiki
Introduction
The Ghost/FreeBSD directory hierarchy is fundamental to obtaining an overall understanding of the system. The most important directory is root or, “/”. This directory is the first one mounted at boot time and it contains the base system necessary to prepare the operating system for multi-user operation. The root directory also contains mount points for other file systems that are mounted during the transition to multi-user operation.
Source: FreeBSD Handbook Chapter: 3.5. Directory Structure
A mount point is a directory where additional file systems can be connected to a parent file system. This is further described in FreeBSD Handbook Section 3.6, “Disk Organization”.
See also Standard Mount Points.