A name is a label for a cell or range: TaxRate instead of $B$1, Prices instead of $C$4:$C$9. Formulas read better (=C4*TaxRate), and a name always points at the same cells, so it behaves like an absolute reference when you fill.
The quickest way to make one is the Name Box, left of the formula bar:
- Select the cell or range.
- Click the Name Box, type the name and press Enter.
Names start with a letter or an underscore, have no spaces, and can't look like a cell address (so not Q1 or TAX2026). Typing an existing name in the Name Box jumps to its range; selecting the range shows its name there. Formulas > Name Manager lists, edits and deletes them.