STUFF()

The STUFF() function deletes a part of a string and then inserts another part into the string.

Syntax: STUFF(string, start, length, new_string)

string: The string to be modified
start: The position in string to start to delete some characters
length: The number of characters to delete from string
new_string: The new string to insert into string at the start position

SELECT STUFF('SQL is important', 5, 2, 'is really ');

Output:
SQL is really important