A mount point can be simply described as a directory to access the data stored in your hard drives.
In more specific terms, a mount point is a (usually empty) directory in the currently accessible filesystem on which an additional filesystem is mounted (attached).
A filesystem is a hierarchy of directories—sometimes called a directory tree — for organizing files on a computer system. With Linux and other Unix, the root directory at the very top of this hierarchy. The root directory includes all other directories on the system, as well as all their subdirectories. The entire hierarchy of directories (the directory tree) found on a single partition or disk is also called a filesystem.
The mount point is used as the root directory of the filesystem, and that filesystem is accessible from that directory. The previous content of that particular directory become invisible and cannot be accessed until the filesystem is unmounted (detached).
Mount points are often confusing to new Unix and Linux OS users because they have not had to worry about mounting with Microsoft Windows OSes. Windows does not require user mounting, but you also have a lot less flexibility in system configuration.
The term itself is confusing in that it suggests there is a point involved, when you are really dealing with a directory. It’s also confusing because directories are usually thought of as containers for holding other directories and files and not as points.
The idea of a mounting point makes more sense when directories are thought of as nodes, that is, as points on a directory tree of a filesystem from which other directories and files branch off.