ㅇ, pronounced 이응, is the hangul letter used for two purposes:

• Before a bare vowel, as in 이 or 아.
• At the end of a syllable, such 랑 or 행. In this case it is pronounced like the English 'ng'.

Adding ㅇ to the ends of syllables which normally wouldn't have it can make them sound cutesy, like so:

• 넹 (from 네)
• 가용 (가요)
• 합니당 (합니다)