The activity of defending or sustaining a principle or a point of view (individual/ general/ of an organization) before a governmental institution or before the law.

The advocacy activity implies:
*the defence of fundamental principles: human rights, freedom of speech etc.
*the education of public opinion regarding a certain disposition/ legislative initiative 
*the presentation before the law of an individual/ general/ of an organization point of view 

What is the difference between lobby and advocacy?

Lobby means to promote certain individual interests, or those of a group or of an organization, by influencing the public politics, the governmental institutions or the law. As a paradox, to lobby always means to advocate, but in the advocacy practices is not always necessary to lobby.

The difference between lobby and advocacy implies direct communication with the law representatives and the public opinion of an individual/ general/ organizational WITHOUT to necessary ask for a legislative modification.