Resonance of waves

A Wave has characteristic features like amplitude, frequency etc.. Now the amplitude of a wave can be increased without increasing the frequency or the frequency can be increased without increasing the amplitude. The increase in amplitude with the increase in frequency is resonance(not the actual definition).

Resonance occurs when the frequencies of two bodies match.

Examples:

1.  When a vibrating tuning fork is kept on a surface of  wood, we hear a loud sound. This is because of resonance. The amplitude of the fork increases suddenly and thus we hear a louder sound.
2. When loud bass(pronounced as 'base') music is played, the glasses around you start vibrating.
3. If you take two guitars both tuned the same and place them side by side, when you pluck the A string on one guitar you will see the A string on the other guitar start to vibrate as well. 
4. When two pendulums of the same length are kept next to each other and one of the pendulum is made to vibrate, then the other pendulum also vibrates.

These are simple examples of resonance.