NT Lan Manager. These days mostly used in an authentication context, since NTLM is the "secure" authentication method used by Internet Explorer against Microsoft web servers (it is essentially a hashed key, the cryptographic meanderings of which I am not at ease to digress upon at 2AM).

As far as secure HTTP authentication goes, it's probably not that hot these days, but most people don't bother to do the right thing and use SSL (even if with self-signed certificates).