A Teaching credential is what you need in order to legally teach in a jurisdiction. It's also commonly referred to as teacher certification or teacher licensure.
In the United States, all 50 states, plus Washington D.C. and Puerto Rico, require teachers to have a teaching certification in order to teach at public schools, just to give you an idea how important they are and how limited your options will be without them.
Traditionally, a teaching certification is obtained by completing a four year Bachelor of Education in-person at a university. However, the rising popularity of the alternative teaching certification means there are now different ways to obtain this credential. This is commonly referred to as alternative certification.
Not sure what a teaching license or credential is? Check out this article.