But the consensus seems to mean a wine that has some residual sugar in it, not one that is fortified. In other words it is sweet, but naturally so, and not very.

As to the definition in terms of the sugar level, this varies too:

"Abocado
Calificativo que se aplica a los vinos blancos dulces que contienen azúcares naturales residuales (restos entre 5 y 15 gr./litro) pero menos azucarados que los licorosos propiamente dichos. También recibe este nombre la degustación de un vino en el que la untuosidad domina a la acidez, aunque sea seco."

http://www.diccionariodelvino.com/index.php/abocado/

"The EU “medium dry” designation covers wines with up to 12 grams per liter. This is demi-sec in French, halbtrocken in German, abbocato (literally, “palatable”) in Italian and either semiseco or abocado in Spanish. The “medium sweet” level (12-45 grams) translates as moelleux (“mellow”) in French, lieblich (“lovable”) in German, amabile (also “lovable”) in Italian, semidulce in Spanish and amado (you guessed it, “lovable”) in Portuguese. Wines over 45 grams are “sweet,” doux in French, süss in German, dolce in Italian, dulce in Spanish and doce in Portuguese. The French term liquoreux refers to wines, often botrytized, that present themselves as syrupy sweet (the Italian liquoroso, on the other hand, connotes a strong, usually fortified wine as does the Portuguese term licoroso)."

http://www.stylegourmet.com/wine/wlang002.htm

"Spanish term used to describe a wine which cannot quite be classified as Sweet but which has certain sweetish flavour. Also Embocado "

http://www.delhiwineclub.com/Glossary/winebasics.asp#