NTFS links are the abstraction used in the NTFS file system—the default file system for all Microsoft Windows versions belonging to the Windows NT family—to associate pathnames and certain kinds of metadata, with entries in the NTFS Master File Table (MFT). NTFS broadly adopts a pattern akin to typical Unix file systems in the way it stores and references file data and metadata; the most significant difference is that in NTFS, the MFT "takes the place of" inodes, fulfilling most of the functions which inodes fulfill in a typical Unix filesystem.
In NTFS, an entity in the filesystem fundamentally exists as: a record stored in the MFT of an NTFS volume, the MFT being the core database of the NTFS filesystem; and, any attributes and NTFS streams associated with said record. A link in NTFS is itself a record, stored in the MFT, which "points" to another MFT record: the target of the link. Links are the file "entries" in the volume's hierarchical file tree: an NTFS pathname such as \foo.exe or \foobar\baz.txt is a link. If the volume containing said pathnames were mapped to D: in a Windows system, these could be referenced as D:\foo.exe and D:\foobar\baz.txt. (Compare and contrast with typical Unix file systems, where a link is an entry in a directory—directories themselves being just a type of file stored in the filesystem—pointing either to another link, or to an inode.)