a loud outcry: the desperate, involuntary cry of a person in pain, terror, or under injustice, calling out to be heard and helped
An outcry is a loud, involuntary cry forced out of a person by pain, terror, or wrong. It is not quiet weeping or shed tears (that is בְּכִי); it is a public shout, and it is always aimed at someone, a cry meant to reach a person who can step in and do something about it.
That gives the word two directions. Most often it is the cry of the wronged: the outcry of Sodom's victims, of Israel enslaved in Egypt, of the widow and orphan, of the poor cheated by their own neighbors. Scripture treats this cry almost as a legal appeal, and it carries a striking promise, that God himself hears it and comes down to rescue those who have no other help. The other direction is the raw wail of disaster: Esau's bitter cry over a lost blessing, the shriek that went up across Egypt the night the firstborn died, the panic of a city as judgment falls.
The prophets turned the word back on God's own people. In Isaiah's song of the vineyard, God looked for righteousness and found instead this outcry, the very sound Israel had once raised in Egypt now rising from inside her own gates against her. Its near-twin זְעָקָה is almost the same word for the same cry, so alike that the writers set the two side by side and even swap them within a single passage.