DAX function

CONCATENATE & — DAX function reference

Join text values.

Syntax

dax

CONCATENATE(<text1>, <text2>)    <text1> & <text2>

dax

"Region: " & SELECTEDVALUE(Region[Name])

→ Joined text

dax

SELECTEDVALUE(Product[Category]) & " — " & FORMAT([Total Sales], "$#,##0")

→ "Bikes — $128,400"

Shows why & is preferred for joining anything beyond two values.

dax

CONCATENATE(Customer[FirstName], CONCATENATE(" ", Customer[LastName]))

→ Nested CONCATENATE needed for 3+ pieces of text

CONCATENATE() takes two arguments; the & operator chains more.
CONCATENATE() is strictly two arguments — joining three or more values requires nesting calls, whereas & chains any number of values in one expression, which is why almost nobody uses CONCATENATE() directly in practice.
& implicitly converts non-text values (numbers, dates) to text using the default format — wrap numeric values in FORMAT() first if you need specific formatting in the concatenated string.

From Text