Questions about relationships like these are quite common. If you’ve ever been in a long-term committed relationship, you’ve likely heard the term “open relationship”.
In an open relationship, a couple is non-monogamous and can date other people as well. Both partners can date other people, or there can be a consensual agreement where one partner maintains only the committed relationship while the other has an open relationship.
This is different from poly relationships because polyamory refers to situations where everyone involved is in the same relationship, but in an open relationship, you date people outside of your relationship.