Lechem oni is the first name for matzah that we encounter on Seder night, when we declare Ha lachma anya, This is the bread of poverty, and invite the needy to share our meal.
Rabbi Joseph Soloveitchik (1903-93) wrote that this is a pledge of solidarity among the Jewish people. By sharing in the bread of suffering, we affirm our brotherhood with all in need, whether the hungry needing food, or the lonely craving company.
Many have remarked on the paradox, that matzah is described as both lechem oni, the poor, rough bread, that our ancestors were fed as slaves in Egypt (because its a cheap way to fill your stomach, according to one commentator), and as the bread of freedom which they ate on their way out.
The Maharal of Prague (1525-1609) suggested a famous resolution. When we are encumbered by superfluities, symbolised by the puffiness of bread, it is difficult to make a break from oppressive conditions. The simplicity that matzah denotes enables freedom.
The Talmud (Pesachim 36a) punningly construes lechem oni as bread upon which we answer (onim) many things. This is not the literal meaning of lechem oni but it captures a vital feature of the matzah. It is meant to provoke us to conversation, to questions stimulated by its strangeness, and multiple answers that draw us into the timeless story of the exodus from Egypt, formative for Jewish identity to this day.