When referring to a 1911, "with rails" almost always (in my experience) means a tactical rail under the barrel/slide to allow you to mount a light or laser. For example, see the Kimber Tactical Entry II (see pix). You won't find these on any older 1911s, they are a fairly recent addition to this genre (maybe last 10 years or so?) I have 4 1911s, 1 with rails (the Kimber pix) the others without (Kimber, Dan Wesson, S&W). The rails are nice if you want optics, and another option is a laser integral with the grip (I have one of those in a 1911, Kimber Classic Royal, and another in a S&W M&P40).
All other things being equal, in a new model 1911 the tactical rail will add $100 to $200 to the retail price.