LOE is something new West Point came out with last year. It's a Letter of Encouragement. It's not effectively a guarantee of an appointment like a LOA (assuming all conditions are met) but more of way of telling you that WP thinks you have a strong file and it also allows you to make an overnight visit to WP (at your expense) before the appointment go out in Feb/March. Normally candidates can only make day visits without an appointment or LOA but with them going out so late now to everyone, they simply can't accommodate all the candidates who would like to then visit in March/April before the deadline. So as said earlier, it's not a guarantee at all but is a good sign.
It's essentially your offer of appointment. A rejection is generally a letter that says "no" in a thin white envelope, whereas your admissions packet takes up a lot of room, making the envelope big and fat. Big fat envelope.