What is series connection of resistors,and what is parallel connection of resistors?

(N/A) Series connection: When resistors are connected end-to-end such that the same current flows through each resistor,the connection is called a series connection. In this case,the total resistance $R_{eq} = R_1 + R_2 + ... + R_n$.
Parallel connection: When resistors are connected such that the potential difference across each resistor is the same,the connection is called a parallel connection. In this case,the equivalent resistance is given by $\frac{1}{R_{eq}} = \frac{1}{R_1} + \frac{1}{R_2} + ... + \frac{1}{R_n}$.