If you have a balance on which you are making minimum payments, then you are using the card.
No usage means nothing happening at all - either new charges or payments on old charges - for an extended period of time. Synchrony/Amazon has been known to notice this after about six months in some cases, and certainly after a year of complete silence they are known to kill the accounts. Presumably it is so that they can prevent potential fraud on inactive accounts (if a person never uses the account for years and then someone charges to it fraudulently, the account holder is less likely to notice until the first payment is overdue and they get called to ask why). If you have a balance on your card, even if you don't buy anything else for over a year, your account is still active while you make your payments.
