What to call all single people?

What to call a group of people in the society which are all single (meaning not being in relationship). Singles?

Singles is a common word for this:

https://www.merriam-webster.com/dictionary/single (first noun definition)

Single people also works just fine.

I hear the term singles a lot when talking about events designed for single people to attend, such as a Friday Singles Mixer, but it works in any context.

Example usage:

I invited my friend out dancing on Friday. It's just for singles, so hopefully we'll meet some great people!

Note that it's uncommon to call just one person "a single", but when referring to a group of single people, calling them "singles" collectively is correct. When referring to one person, you'd use the adjective single ("he is single", "I am single", etc).

You could refer to them as unattached.

adjective: not married or not having a relationship with anyone; single

You could call them "unattached people".

In my experience, you would also be understood if you used it as a noun in the same way you would use "singles". As in...

I have started a dating service targeted at the unattached.