Resistance is like the width of a pipe; a narrow pipe (high resistance) makes it harder for water to flow, just as a material with high resistance makes it harder for electrons to pass through.

VIR: $V = I \times R$, where $V$ is voltage, $I$ is current, and $R$ is resistance.

According to Ohm's Law, the resistance $R$ of a conductor is defined as the ratio of potential difference $V$ across its ends to the current $I$ flowing through it. One Ohm is defined as the resistance of a conductor when a potential difference of 1 Volt causes a current of 1 Ampere to flow through it ($1 \Omega = 1 \frac{V}{A}$).

Always remember the difference between unit and property; resistance is the property, and Ohm is the measurement unit. Exams often confuse these with current ($I$) and potential ($V$).