연등이 · 연등을
lotus lantern (lit for Buddha's Birthday)
Example
부처님 오신 날에 절에 가서 연등을 달았어요.
On Buddha's Birthday, I went to a temple and hung a lantern.
Word parts
연 burn+등 lamp
Literally 'burning lamp'. The 연 is 'burn', not 연꽃 'lotus', even though many lanterns are lotus-shaped.
Good to know
Every spring Seoul holds 연등회, a lantern festival and parade, ahead of Buddha's Birthday.