I got a new pair of shoes, so I think I'll use the old, second string pair in my garden.
(Spor) The group of players that substitute for the starting players or from which substitute players are drawn on a sports team
If you describe a person or thing as someone's second string, you mean that they are only used if another person or thing is not available. a second string team
{s} being a substitute or replacement for a regular player (as on a team in sport games); available as a second choice