What does the -d option in the cut command allow you to specify?

The -d option in the cut command allows you to specify the delimiter that separates the fields in the input file. By default, cut uses a tab character as the delimiter, but you can change it to any character you want.

For example, if your file uses a comma as the delimiter, you would use:

cut -d ',' -f1 filename.txt

In this case, the -d ',' option tells cut to treat commas as the field separator.