Branch: A two-terminal element is regarded as a branch, and there are as many branches as there are two-terminal elements in the circuit. Three-terminal or more elements are not considered here because they are not included in the simple circuit analysis.
Node: the connection point between branches and the connection point between two double-ended components.
Loop: A closed path consisting of branches.
Mesh: A loop with no branches on the plane circuit diagram. For a connected circuit with B branches and N nodes, n- 1 KCL equation, node current equation, b-n+ 1 KVL equation, mesh equation and VCR equation (volt-ampere characteristic equation) with B linearity independence can be listed. There are (n-1)+(b-n+1)+b = 2b equations. So this method is called 2b method. Using 2b method to solve circuit problems requires almost no brains, and the equations can be listed soon. However, this method involves many unknowns and it is easy to make mistakes in solving equations, so this method is not used in solving problems. However, 2b method is the most basic method to solve the problem of linear resistance circuit, and other methods are obtained through certain mathematical transformation and the use of other auxiliary formulas. Therefore, it is necessary to deeply understand this method and its connection and difference with other methods.