'Effacement' is the thinning of the cervix. Dialation is the opening of the cervix.
i dont know the exact defintion of effacement, but i thought it meant labor was right around the corner, i was wrong, i was 80% effeced and 3 cm for 10 days before i delivered, my doctor said he stripped me, even when i was already 80 %, and said labor would happin within 72 hours, wrong again, but ive heard many people efface a lot faster than i did, but the good thing about it was that when i did get to the hospital i was 100% effaced and 5 c, 3 hours later dd was born! i think labor went quickly because i didnt have to efface anymore, so if it does take you a long time hopefully your labor is quick!