오늘이 · 오늘은 · also used as an adverb (오늘 뭐 해요?)
today
Example
오늘은 날씨가 좋아요.
The weather is nice today.
Word parts
오늘, 어제, 모레 are native; 내일 (tomorrow) is the odd one out — it's Sino-Korean.
Good to know
Can stand alone without a particle: 오늘 바빠요? = Are you busy today?
Related words