Friends-
An indoor water supply valve to an outdoor spicket is leaking around the base of the stem when I open the valve to use the outdoor faucet. Is it most likely from a deteriorated washer or O-ring? Is this corrected by turning off the house water supply, opening the outdoor faucet to drain the pipe and opening the cover around the stem? I apologize if using the wrong terms. Thanks for your time and wisdom.
Paul McC

"Packing" is what you need. Here's an explanation from a recent post re the same leaking from around the stem:
https://www.askmehelpdesk.com/plumbing/faucet-behind-washer-leaks-24569.html?highlight=packing

Rick gave you very good advice along with link to a faucet, (let me make it easier for you, see image) He correctly identified your problem as a water leak at the bonnet packing nut. Try this, open the faucet up a bit and when the water begins to leak past the stem snug the bonnet packing nut up until the leak stops.
If that don't get it then you may need to replace the bonnet packing itself.
Good luck, Tom