What is the meaning of 第?

ordinal marker, often with affix 号

chữ Hán form of đệ

1. ordinal number marker, used only to mark the generation of a person who shares their name with their parents or grandparents, equivalent to the use of I, II, III, etc. in English.
2. ordinal number marker in general

   ordinal number marker, used only to mark the generation of a person who shares their name with their parents or grandparents, equivalent to the use of I, II, III, etc. in English.

   ordinal number marker in general

   Source: wiktionary.org