If you want to add tags or keywords to a sheet, or something like a pick list but with multiple selections allowed, you can do this with a linked sheet.
For example, suppose you want to add tags to your Contacts sheet:
1. Create a new sheet named Tags.
2. In the first row of this sheet, add the tags, one per line.
3. On your contacts sheet, click “Link Sheets” and choose Tags:
4. This will create a Tags column in your sheet where you can add multiple tags:
5. You can then search your sheet by tag with searches like these: