What does 第～ mean?
第～ is a Japanese prefix meaning “ordinal prefix (No. ~)” in English. It is written as 第～ in kanji, だい～ in hiragana, and dai～ in romaji. This word is part of JLPT N3 vocabulary.
NotePrefix that makes ordinal numbers (第一 = first, 第五課 = lesson five).
Example sentences
第二次世界大戦は1945年に終わった。
The Second World War ended in 1945.
今日は第五課を勉強します。
Today we're studying lesson five.