What does "plenty more fish in the sea" mean? Is it an idiom?

Rebecca

"Plenty more fish in the sea" is an expression that means that there are more eligible people out there for single people to date. This is usually said when a relationship or an interest doesn't work out. A: My boyfriend and I broke up a month ago. B: I'm sorry, but hey, there are plenty more fish in the sea! Ex: There's always more fish in the sea.