String is a type of data, and it’s basically just any kind of text.
You can recognise a string because they’re always eclosed in single or double quotation marks.
"Hello there"
is a string'Hello world'
is a string"123"
is a string123
is not a string but an integer, which means whole number.
So next time an application, API or whatever asks for a string, they basically just mean any kind of text (and not a number).