What is meant by eminent domain?

Eminent domain is the right of the government, its agencies, and certain monopolies to take private property, especially land, for public use subject to reasonable compensation.

For example, if the community school is no longer large enough to accommodate the growing population, and you are the farmer who owns the adjacent field, then the government can take the necessary portion of your field which would be required for an school expansion project even against your will. However, you have the right to fair compensation.