Yes, it is. After all, you wouldn’t be able to create multiple profiles if Netflix accounts were limited to a single person. However, some terms apply. According to Netflix’s ToS, your account ...

Learn the signs of a hacked Netflix account and get step-by-step guidance to regain access and secure your streaming profile.

In the US, according to Netflix's help site, adding an extra member with ads costs $7 per month, and the option is available alongside the pre-existing extra member accounts that do not have ads.