What are Minimal Pairs?

What is a Minimal Pair?
A minimal pair is a pair of words that differ only in one sound. 
For example:
BAD BED
BIT BEAT
THINK THING
FAT HAT
SINK THINK

Why is it important for EFL students to learn Minimal Pairs?
Because just by mispronouncing ONE sound, we may change the meaning of a word completely. Our interlocutor may not understand what we mean or may be really confused.

One, two, three! 

or
One, two, free!