Implicit-
adjective 1.
implied, rather than expressly stated: implicit agreement.
2.
unquestioning or unreserved; absolute: implicit trust; implicit obedience; implicit confidence.
3.
potentially contained (usually followed by in): to bring out the drama implicit in the occasion.
4.
Mathematics. (of a function) having the dependent variable not explicitly expressed in terms of the independentvariables, as x2+ y2= 1. Compare explicit(def. 6).
Explicit-
adjective 1.
fully and clearly expressed or demonstrated; leaving nothingmerely implied; unequivocal: explicit instructions; an explicit act of violence; explicit language.
2.
clearly developed or formulated: explicit knowledge; explicit belief.
3.
definite and unreserved in expression; outspoken: He was quite explicit as to what he expected us to do for him.
4.
described or shown in realistic detail: explicit sexual scenes.
5.
having sexual acts or nudity clearly depicted: explicit movies; explicit books.
(definitions from www.dictionary.com)
Implicit rules are rules are rules that are not directly spoken or stated, while explicit rules are directly stated.