Definition

A phoneme is a linguistic concept that means a sound that also has a meaning in a language. For example, [p] and [b] are articulated in the exact same way in the mouth - the only difference is whether or not the vocal chords are vibrating, resulting in a voiceless [p] or voiced [b] consonant. In English, however, these two sounds are recognized as being different and have an affect on meaning. For example, pat and bat. In Korean, these sounds are NOT recognized as being different in meaning although you will hear both sounds being made such as in the word 바보 [p]a[b]o (which means fool). 

This is actually a relatively common and simple voicing pattern in many languages, including Korean. This effect occurs with the English plural marker, -s. Non-native speakers more obviously hear [s] and [z] (such as cat[s] and dog[z]) whereas native speakers do not hear/interpret any difference.