The book An Introduction to Quantum Computing (section 10.4.1 Error Models for Quantum Computing) by Phillip Kaye, Raymond Laflamme and Michele Mosca states the following:
Errors occur on a qubit when its evolution differs from the desired one. This difference can occur due to imprecise control over the qubits or by interaction of the qubits with an environment. By ‘environment’, we mean everything external to the qubit under consideration. A ‘quantum channel’ is a formal description of how qubits in a given setting are affected by their environment.
I would like to know what is the environment and what are the physical characteristics that describe it.
Furthermore, does the qubit alone generate noise within itself (assuming that no noise is generated from its environment)?