In electrical engineering, an unbalanced circuit is one in which the transmission properties between the ports of the circuit are different for the two poles of each port. It is usually taken to mean that one pole of each port is bonded to a common potential (single-ended signalling) but more complex topologies are possible. This common point is commonly called ground or earth but it may well not actually be connected to electrical ground at all.
Unbalanced circuits are to be contrasted to balanced circuits where the transmission paths are impedance balanced (the impedances are identical).