To me, it means
1)Standing with a country or a people against outside intervention(military or political), and being willing, if necessary, to put one's own body on the line against such intervention;
2)Denouncing any attempts to coerce an outcome those people or that country do not wish to see, and acting(including actions of civil disobedience if necessary)to impede the efforts of those working against the cause or people in question;
3)Providing material and monetary assistance, if needed, to those who one stands in solidarity with; breaking economic embargoes against the people or cause in question if such embargoes exist;
4)Visiting the area where the people you are in solidarity with are living and struggling, living there for extended periods of time if doing so is a helpful thing, and doing what you can while you are there to help the people or the cause(especially, to help the ordinary people and those in the rank-and-file of the cause in question, if not so much those in the leadership):
it does not require silenct acquiescence in actions or practices that go against my values as a leftist, a person who shares both humanist and progressive religious values, or simply a decent human beings.
It does NOT require anyone to defend things in one situation that a person wouldn't defend in others(especially if a person wouldn't defend those things in their own country).
Finally, I believe that, If spoken in a supportive, nurturing, positive vein, in the name of defending the larger cause, critical comment about the actions of the leadership, or suggestions for alternative courses of action when one course of action seems futile, when such comments are spoken by a person IN solidarity(as opposed to a person acting as a enemy of the cause)can be the HIGHEST form of solidarity-the solidarity of respect and the solidarity of truth.
The worst mistakes the Left has made in the past were when it equated dissent with disloyalty(something we rightly reject when the forces of reaction make such an equation). The greatest and most useful form of solidarity we can display is the solidarity that says "I'll stand with you...but I follow no one blindly, and I accept nothing without question...because I respect all people and believe that all people deserve to be treated with dignity...and believing that means I must be honest when I support a cause, but see where the cause may be going wrong".
All of the above, to me, is solidarity. What does it mean to you?
I'd like to have a respectful discussion on this, with people on whatever sides emerge being willing to listen to what each other has to say.
If nothing else, we can agree that there can be many forms OF solidarity.