Please advise what function it is

[MaySeng]

Saw this in function in the previous file created by my ex-colleague. Apprecite if anyone can advise what is the function and how to create it. 

Question

[#2]

@MaySeng 

That is data validation.

https://support.microsoft.com/en-us/office/apply-data-validation-to-cells-29fecbcc-d1b9-42c1-9d76-ef...

https://www.contextures.com/xldataval01.html

[#3]

Hi @MaySeng 

it is called a drop down list.  here's a link showing how it is created using the data validation in the toolbar ribbon:

Create a drop-down list - Office Support (microsoft.com)

cheers