[Potentially NSFW] What do you consider an affair (in the sense of interpersonal relationships)?

I was discussing this with someone at dinner on Tuesday.

What do you consider an affair? What qualifies?

- one time hook-up? With a random person or someone you know?

- multiple meets over time, meaning longevity and consistency?

- Do affairs need to include a physical element (i.e. sex), or can they be verbal or mental without anything sexual happening?

- Can LTRs be considered affairs? What about cybersex and internet-hosted relationships?

- Do affairs imply the involvement of emotions and love, or can they be physical only?

- Is a FWB situation an affair?

- Does there have to be a third party (the unknowing husband or wife) for a relationship to be considered an affair?

Etc…